FORTH on the Atari Learning by Using

5/19/2018 FORTH on the Atari Learning by Using

1/132


2/132

This

book

is

an

independent

production

of Ing. W.

HOFACKER

GMBH International. It is published

as

a service to all ATARI per

sonal

computer

users

worldwide

.

All

rights reserved. No part

of

this

book

may

be

reproduced

by

any means

without

the express

written

permission

of

the publisher.

Example programs are for personal use only. Every reasonable

effort has been made to ensure accuracy throughout this

book

but neither the

author

or publisher can assume responsibil ity for

any errors or omissions. No lia

bility is

assumed

for

any direct or

indirect damages resulting from the use

of

information contained

herein.

First

Edition

First Printing

February 1983 in the Federal Republic

of

Germany

Copyright

1982

by Winfri

ed Hofacker

Order-

No. 17

IS N

3 88963

-

170

-3

Reference was made to

AT

A R I throughout t hi s book.

ATAR

is a

trad

emark of

ATAR I Inc a

di

vision

of

Warner Communica

ti

ons Company.

Publ i

sher

Ing . W. HOFAC KER Gm bH . T

ege

rnseerstr . 18 .

0-8

150 Ho lzk

ir

ch

en

. W

.

Germany

US Distributor:

E LCOMP Pu b li sh ing. Inc .. 53 Redrock Lane. Pomona

CA

9 1766


3/132

T BLE

OF

CONTENTS

1 What is FORTH . . . .

. . .

. . . . . .

. . 1

2. Basic elements of FORTH . .

. .

. . . . . . . 4

2-1 The stack . . . 4

2-2 Words in FORTH . . .

. . .

.

.

. .

. . .

6

3

Using words . . . .

. .

. . . . . . . .

. . . . . 9

3-1 Definition of new words . . . . . . . .

. .

. . . . . . . . 9

3-2 Changing the stack .

. . . .

10

3 3 Fundamental operations in arithmetic . . . 12

3 4 Input output . . . . . . .

. .

13

3-5

Some simple programs

. .

.

15

3-6

The

screen

. .

. .

. . .

. . . .

. . . . . . . .

. 19

3-7 Constants and variables . . . . . . . . 21

3-8

Comparison . . . . . . .

. . . . . .

. . . . .

24

4 Control structures 25

4-1 DO .... LOOP . . . . . . . .

. .

. . . . . . 25

4-2 The return stack

. .

.

. . .

29

4 3 IF .ELSE ....THEN ENDIF) 30

4-4 BEGIN UNTIL . . . . . . . 32

4-5 BEGIN .WHILE ... REPEAT . 33

4-6

The

case statement . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5

Sample programs . . 35

5-1

Some grafics

. . .

.

.

.

. .

.

35

5-2 Pattern

. .

. .

. . .

. . . . .

. . .

. . . . . . . . . . . . . . . . . . . .

41

5 3 Sound and color . . . . . . . . . . . . 42

5-4 Hexdump . . . . . . . . . . . . . . . . . 46

5-5 Largest common divisor . . .

. .

.

48

5-6 F ibboconacci numbers . . . . . . . . .

. . . . . . . . 50

5 7 Prime numbers . . . . . . . . . . . . 52

5-8

More sound and grafics . .

.

. .

.

53

5-9 Using the game

port for

control app lications

. . .

. . . 55


4/132

6. Text and strings 64

6 1

INPUT/OUTPUT

of text

.

64

6 2

Formatting the

output

. . 70

7.

The vocabulary .

. .

.

.

74

7 1 Different vocabularies .

. .

. . . . . 74

7 2 Play organ

or

piano

with

the

ATAR

I 76

7 3 The construction of a FORTH

word

80

7 4

Changing the

top of

the

dictionary

.

. 84

7 5 The virtual memory . . 88

7 6 Definition

words . . . . .

91

8. Applications .

. .

.

95

8 1

Mailing list .

. .

. . . . . 95

8 2 Serial output via game port three . . . . . . . . . . . . . .

107

9.

Appendix

. 114

A FORTH-compiler/interpreter is available from the

following

vendors:

1 ELCOMP

PUBLISHING

INC. Pomona CA 91766

Phone 714) 6 2 3 ~ 3 4

2.

Quality

Software

6660

Resede

Blvd. Suite

105,

Reseda

CA 91335, Phone 213) 344-6599

Books and source code

information are

available

from:

1. FORTH

Interest Group

P.O.Box 1105

San

Carlos

CA

94070

2. Mountain View Press

P.O.Box

4656

Mountain View CA

94040

3. FORTH Inc.

2309

Pacific Coast

Hwy.

Hermosa Beach CA 90254


5/132

PREFACE

ATARI FORTH PROGR MMING

Learning by using

FORTH

i s

a

new,

exc i t i ng

programming

language. I t i s easy to l ea rn and programs,

wri t t en

in

FORTH are very sh o r t

compared

to o ther high l eve l languages.

The

aim of t h i s book i s to show

the

novice

and the exper ienced

programmer

how to

use

t h i s

language

on

the

ATARI

The

examples

are shor t and

use

sound and

gr a f i c s

for

demonst ra t ion .

Use

these examples

to

lea rn

FORTH

Two

a p p l i c a t i o n s

a

mai l ing

l st and a

s e r i a l i n t e r f ace for a p r i n t e r are

inc luded . These two app l i ca t i ons show the

wide

v a r i e t y

FORTH

can

be

used

fo r .

With

FORTH

an app l i ca t ion

can

and

debugged

f a s t e r

than in

programming language.

be

wri t t en

any other

I

hope t h i s

book

wi l l add new

f r i ends to

the

community

of

FORTH

programmers.

Thank s

to Rick Schwarz, who helped me

in

proofreading .

E.Floege l


6/132


7/132

VVhatisFORTH

1

WH T

IS

FORTH?

FORTH i s l i ke BASIC, FORTR N or PASCAL a

programming

language

I t

i s , however

qu i t e

d i f f e r en t

from these l anguages . I t was

invented

by CH RLES MOORE about t en years

ago and

i t s

f i r s t use

was to

con t ro l

t e lescopes

on

t he

Ki t t

Peak

observa to ry .

Today

FORTH i s widely used in

con t ro l

app l i ca t ions . One example

i s

the con t ro l

of movie

cameras in the

movie

BATTLESHIP

GALACTICA Using the concept of v i r t u a l

memory, FORTH a l so i s used for da ta base

managment

FORTH

can

not be compared

with other

programming

languages While you

are

learn ing to program in FORTH t would be

be t t e r to fo rge t a l l you have l ea rned

about

othe

r

languages .

What makes FORTH so unique ?

One of the bas ic elements of FORTH i s the

s tack . Everybody knows what a

s tack i s .

Nearly every desk

has a s tack of paper .

Something i s

l a i d upon

t h i s s tack and may

be

removed

l a t e r

In

terms of a computer

t h i s i s a

LIFO

Last I n , F i r s t

O u t

memory

The

l a s t

th ing

put

onto

the s tack

i s

removed

f i r s t .


8/132

FORTH uses the s tack in

two d i f f e r en t

ways.

F i r s t t he re i s

a

parameter

s tack

for da ta

and

ca l cu l a t i ng . Second t he re i s a s tack

for

words ca l l ed

the d ic t ionary or

vocabulary .

In

FORTH

words

are

the

elements for programming.

Severa l of

these

words can be combined to form a new

word

performing a

ce r t a in

t a sk . A

bas ic

d ic t ionary

of

predef ined

words i s

conta ined with in FORTH.

These

words

are

used by

the

programmer to

c rea t e

new words.

This

new

words

are

placed

on

top

of

the

d ic t iona ry .

Running a program in FORTH

means

ca l l i ng

a sequence of words.

For example

you have

wr i t t en a FORTH

program to

con t ro l

s tepper

motors .

START

may be a

word

for

s t a r t i n g the s tepper

motor .

FASTER

SLOWER

may be

words

for

changing the

speed

while

STOP could

be the

word

for s toping it

Defining your own

words

makes FORTH

very

f l ex i b l e . Words can be

rearanged

to

perform new t a sks .

All t h i s makes FORTH a

dynamic language. On

the

o ther hand a l l

t h i s

freedom

makes

the

programmer

respons ib le for

the

cor rec tness

of a

program. There are only a few er ro r

messages

and warnings .

Though FORTH i s used sometimes

with other

opera t ing systems it could be

seen

as i t s

own opera t ing

sytem. I t i s an

i n t e rp re t e r

ca l l i ng and execut ing one word. I t i s

a l so

a compi ler

with i t s

capab i l i t y to

compile

new words in

the

d ic t i na ry .

I t

uses a

t ex t

e d i t o r

and

of t en

an

assembler .

In t h i s bookle t we wi l l l ea rn FORTH by

using t h i s

language

on

an

ATARI

400/800.

We wi l l use

graph ics

sound and j oys t i ck s .

2


9/132

All programs

however,

which don t use

specif ic hardware on the

T RI

can be

easi ly

adapted

to

other computers.


10/132

asic

l m nts

of

ORTH

2 .

BASIC

L M NTS

OF

FORTH.

Let us

f i r s t

make some remarks concerning

the

bas ic

elements

of

FORTH.

2-1

TH

STACK.

As

mentioned

above

the

s tack

i s

a LIFO

memory. In Fig

2-1 a

s tack

i s represented

in

two ways. Fig 2 l a shows

the

normal

rep resen ta t ion of a s tack . In t h i s book

we

wi l l use the s tack

as

it

i s

shown

in Fig 2-

lb .

TOS

Fig .2-1a

TOS

- .--. .---- --.----r---r------.

- - L _ - - - . l . _ - - J i . . . - _ - - - _ ~ _ - - _ . . . J

Fig.

2- 1 b

Fig 2-1

Two

r ep resen ta t ions of

the s tack .

4


11/132

The top of s tack TOS )

i s

always the

r ightmost element . One

memory

c e l l of

the

s tack

i s a

16

b i t c e l l .

For documentat ion

and unders tanding

of

FORTH

words,

t

IS

necessary

to show

how

the s tack i s

af fec ted by using a word.

We

wi l l use the

fol lowing

abbrev ia t ions :

a 16-b i t address

n s igned 16 b i t

number

u unsigned

16 b i t

number

d s igned 32 b i t number

b 8

b i t

byte

c 7 b i t ASCII cha rac t e r

f boolean number, f l ag

These

abbrev ia t ions are

fo l lowing manner:

used

in

WORD STACK

BEFOR -

ST CK

AFTER )

Examples:

LOOK an)

the

The word LOOK, whatever

t

does , reques ts

an address and a number on top

of

s tack

before execut ing .

Both

i tems

are

removed

from

s tack a f t e r

execut ion .

FOUND - f )

FOUND

doesn t

need any parameter before

execut ion and l eaves a boolean number f

on

the s tack

a f t e r

execut ion .

COMP a a c - nf)

The word COMP

needs

charac te r on

top

execut ion a

number

l e f t

on

s t ack . In

top

of

s tack

i s

two

addresses and a

of

the s tack . After

and a boolean f l ag i s

t h i s r ep re sen ta t i on , the

always

the

r igh tmost

5


12/132

cha rac t e r . To d i f f e r between severa l

addresses or

numbers t he re

can be

added

a

hyphen

or

a

number to the charac te r l i ke

a

a or n n l n2.

2-2 WORDS IN

FORTH.

A

word in

FORTH may be

any a rb i t r a ry

s t r i n g of

charac te r s , excluding

th ree

spec ia l cha rac te r s .

The

excluded

charac te r s

are :

the

space

backspace

and

the re turn

charac te r .

The space

charac te r

i s

the only

de l imi te r

between

FORTH words.

The backspace charac ter i s

used

for

cor rec t ing

typing e r ro r s ,

while

the re turn

charac te r

i s

used to ind ica te t h a t the

input to

the

computer i s f in i shed .

Examples

of words:

FIRST

lTIMES

NAME

@VALUE

THR EE i s

not

recogniced as

because t he re

i s

a space

in it

represen t

two words THR and

EE.

one

word

I t would

Some words in the

predef ined

d ic t ionary

cons i s t of only one

charac te r . The

dot

i s for example the pr in t ing

s ta tement .

The @ s ign fe tches the conten t of a 16 b i t

memory c e l l . These l e t t e r s

can be used

to

i nd ica te

a

spec ia l

funct ion

of

a

word.

In

the

example above

NAME

wi l l

p r i n t

a

name

while

@VALUE wi l l ge t

some value from

memory.

This

naming convent ion makes it

eas i e r to

read

FORTH programs.

2-3 THE

REVERSE POLISH NOTATION.

For

ca l cu l a t i ons , FORTH

uses the reverse

Pol i sh , or pos t f ix nota t ion .

The

opera tor


13/132

for the ca l cu la t ion i s entered

here

a f t e r

ente r ing

the numbers. I f you

type in

36

f i r s t a

t h ree

i s put on s t ack then a

s ix .

At t h i s

t ime,

the

ORTH

i n t e r p r e t e r

recognices

the word + This word takes

the

two

top numbers

on

s t ack adds them

toge ther and

places the

r e s u l t 9 , on top

of

the

s t ack . I f you now

en te r

the

command a 9

i s

disp layed

on

the

screen.

Try

it.

The word +

i s

def ined

in

the fo l lowing

manner:

+ nnl -

n2)

n2=n+nl

Exerc ises :

3*4-7

3*5+3)/6-4

5

A

2-4

A

2

3+5)*2

20/ 2*5)

Using

the reverse

Pol ish

n o t a t i o n

t he re

i s no

need to use bracke t s . Let

us look a t

the

fol lowing example:

3+5)* 4-2)-7

A BASIC


who

has

to

decipher

such an express ion

s t a r t s with the opening

bracke t then

gets

a number, an

opera to r

once

more a

number

and then the

c los ing

bracke t . At t h i s moment it can do the

f i r s t

ca l cu l a t i on .

The next s t ep ind ica t e s

a requirement for

mul t ip l i ca t i on . This can

be done a f t e r

reveal ing the second

express ion .

7


14/132

Using

RPN,

t

i s eas i e r for a

computer

program to ca l cu la t e t h i s express ion . In

RP

we en te r

3 5 4 2 -

7 -

You see t he re i s no need for

bracke t s .

Fig

2-2

shows

the

eva lua t ion

on s t ack .

ST CK

TOS

3

INPUT

3

3

8

8

4

.

8

6

5

8

4

2

2

16

7

9

5

+

4

2

7

Fig

2-2

Calcu la t ing an

ar i thmet ic

express ion

using RPN.

To ge t acquain ted

with t h i s reverse

no ta t ion the re

are

some

exe rc i

se s .

them i n to the compute r

and

use

command

to

ge t

the r e su l t s .

Exerc ises :

8

3*4-7

(3*5+3)/6-4

5 2-4 2

(3+5)

*2

20/(2*5)

Pol i sh

Type

the


15/132

3 sing words

3.

USING WORDS

You can f ind a d ic t ionary

of

a l l common

words

in appendix A. Here we wi l l

discuss

the

most

used words

for

wri t ing programs

in

FORTH.

3-1 DEFINITION OF

NEW

WORDS

The

def in i t ion

of a new

word

s t a r t s

with

the s ign , followed by a space and the

name of the new

word

.

Then

a l l words used

by t h i s new word are l i s t ed . The

def in i t i on ends with t h e ; s ign .

: XXX

Eegin

of a colon

def in i t ion XXX

End

of

a colon

def in i t ion .

Unti l now

we have learned only two

words.

The

word

and the word. We

want to

combine these two to a new

one,

ca l l ed .

plus pr in t . I t adds two numbers and

disp lays the

r e su l t .

The de f in i t i on i s :

:

.

Now

we

can

enter

3 6

. RET

an

d

get

the

r e su l t 9

on

the sc r een .

9


16/132

To show

t h a t

the

opera tors

rea l FORTH words we change the

these

two words

by

+ and - are

meaning of

+ -

After h i t t i n g re turn

we ge t

a warning

ISN T UNIQUE OK

This ind ica tes

t ha t

the

word

al ready def ined . The


the

new def ined

+

When

we

now

RET, we ge t the

r e su l t

3.

+ has

been

wi l l

use

type

3 6

Let us fo rge t t h i s new word. By typing

FORGET

RET

t h i s def in i t i on and

made

l a t e r

on

d ic t ionary .

a l so a l l

def in i t i ons

are

removed

from

the

3-2 CH NGING THE STACK.

The s tack can be changed in t h ree ways. I t

can

be

enlarged,

reduced or

rearanged. All

t h i s can be done

with the fol lowing

words:

10

DUP n -

nn) Dupl ica te

top of s t ack .

DROP n)

Throwaway the

top

of

s tack .

SW P n n - n n ) Reverse the two top

elements .

OVER n n - n n n ) Copy of the second

element

on top .

ROT nln2n3-n2n3nl)

Rotate the top

th ree

elements

counte r

clock

wise

.


17/132

Fig 3-1 shows how these words a f f ec t the

s t ack

2

4

2

4

5

2

4

3

2

4

3

2 4

2 4

3

5

3

3

5

3

5

3

3

5

3

5

3

DUP

ROT

SW P

DROP

OVER

Fig

3-1

Changing

the

s t ack

Now l e t us do some examples and exe rc i s e s

Example

1:

The s tack

con ta ins

the

numbers 3 2 1

with

the

1 on

top

of the

s t ack

What words must

be

en te red to ob ta in the

sequence

3 2 2

I?

F i r s t we

en te r

OVER and ge t 3 2 1 2 .

Second we en te r SWAP to ob ta in the r e su l t

3 2 2

1

Example 2:

On

the

s tack

we

have

3 2 1 with

the

1

on

top

of the

s t ack

Which

words must be

entered to

ge t the sequence 2 3 3

?

The

answer i s shown below.

DROP

SWAP

DUP

Exerc ise :

and ge t

S t a r t

a

b

c

d

e

3 2 1

3

2

2 3

2 3 3

with

3 2

1 on

3 2

2 3

23

23

32 2

the

s tack


18/132

The w o r d . S dot s , p r in t

stack)

shown

in

Fig

3-2

i s very

use fu l l . I t

i s

def ined in

most

of the FORTH vers ions and

pr in t s

the

conten ts

of

the s tack without des t roying

it

I f your FORTH vers ion

does n t know

t h i s word j u s t type it in .

S

SP@ ;

DEEP SO @

S

- 2 / 1 -

.S CR DEEP S 2 -

SO

@ 2 -

DO

I @

-2

+LOOP

ELSE

.

EMPTY THEN

Fig

3-2

Non-des t ruct ive

s tack pr in t .

3-3

FUNDAMENTAL

OPERATIONS IN ARITHMETIC.

The word for the fundamental opera t ions of

ar i thmet i c

are def ined as fo l lows:

+

nnl-n2)

n2=n+nl

nnl-n2)

n2=n-nl

nnl-n2) n2=n*nl

/

nnl-n2) n2=n/nl

This ar i thmet i c i s done with 16 b i t s igned

f ixed numbers.

Finding the

remainder and

the

quot ien t

of

a

def in i t i on

you

can use

two more words.

MO nnl-n2) n2 i s the

remainder

of n /n l .

/MOD nn1-n2n3) n2

i s

the remainder

and

n3

i s

the

quo

t i en t

of

n /n l .

12


19/132

Example:

We want to c a l c u l a t e

the value

of t he

te rm

XA

+ X*y +

Z. The va lues for X,

Y

and

Z

are

s to red

on

the

s tack wi th

Z

on

top

of

the

s t a c k

Fig

3-3 shows t he sequence of

words

to c a l c u l a t e t h i s va lue

x

Y

x

Z

- -

Z

Y

Z

Y

x

z

x

x

Z

x

Z

Z

Y

x

x

Y

X+Y

X X+YI

RG

SWAP

R T

OUP

R T

+

Fig

3-3

Calcu la t ing

the

te rm

XA2+X*Y+Z.

We can

def ine a

word

.VALUE

which needs

t h ree numbers

on

the

s tack

and c a l c u l a t e s

the

value

of t h i s express ion

VALUE nnln2)

SWAP

ROT

DUP ROT + * +

.

,

Exerc i ses :

for

Try to

ge t the

word sequences

a) X

A

2+X*Y-Z

b)

x

A

2+x*Y+Z

A

2

c) X

A

2-X*Y-Z

A

2

with

X Y Z

on

the

s t ack

and

ge t the

r e s u l t s

3-4 INPUT OUTPUT .

I n s e r t

numbers

One of

the output

i n s t r u c t i o n s we

have

a l read

y

used was th e

.

word.

I t

de f i n i t i on

i s :

n)

Pr in t the top of s t ack

13


20/132

Other output i n s t ruc t ions are

:

Example :

Pr in t

message.

The

message ends

with

. HELLO

RET HELLO OK

EMIT

c)

Pr in t s

ASCII

value

c .

Example:

69 EMIT RET EOK

R

SPACE

SPACES

.R

Example:

Pr in t s

one ca r r i age

re turn

.

Pr in t s

one

space .

n) Pr

i n t s n spaces .

nnl) Pr in t n, r i g h t j u s t i -

f i ed

in

f i e l d . Fie ld -

with i s n l .

F i r s t we def ine a word P as

P (

n) 4

R R ;

Now we en te r :

R 1 P 10 P 100 P

and ge t the r e su l t

14

1

10

100


21/132

The fo l lowing

words are

for

da ta input :

KEY

( - c ) Reads the keyboard and

places the

ASCII

value

on

the

s t ack .

?TERMINAL - f ) True

i f

the

break key

i s pressed .

But on

the ATARI:

?TERMINAL -n

n=l ,2 ,4

i f

one

of

the

yel low

keys was

pressed .

n=O

i f

no key was

pressed .

START

key

n=l

SELECT key n=2

OPTION

key

n=4

There are some

more input

and

output

words,

which wi l l be

discussed

l a t e r on in an

ex

ample.

3-5 SOME SIMPLE PROGRAMS

Unti l

now we have l ea rned

only

a

few

FORTH

words, however

they

are

s u f f i c i e n t

to

wri te some simple programs.

3-5a A LANGUAGE TRANSLATOR.

The

concept of the

d ic t ionary and

of

de f in

ing new words can be

used

for a language

t r ans l a to r .

As an example we t r a n s l a t e

some words in to the german

language.

I . ICH ;

AM

.

BI N

;

HERE

.

DA

;

5


22/132

I f we

type

I M HERE

we

ge t

the

t r an s l a t i o n

ICH

BIN

DA

This

i s

only a very simple example.

But

you

can

use

t

to remeber

spec ia l

words in

a fore ign language chemical formulas or

to

make

a

l st

of

your

favour i t e

rad io

s t a t i o n s

and t h e i r

f requencies . For

example:

KBIG

: KIQQ

104 FM

100 FM ;

3-5b WEIGHTWATCHER

Some

peoples

want

to ca l cu l a t e

the

amount

of ca l o r i e s

they had

for breakfas t

or

dinner .

The

input

of

da ta

should

be

done

in the fo l lowing way:

BEER 1 GLAS

COKE

2 GLASSES

BREAD 1 SLICE and

so

on.

The program

i s

shown in Fig .3 4 . F i r s t

t he re

i s

a

comment

ind ica t ing

which

un i t s

of

measuremen

t

are

used for

the d i f f e r en t

types of foods. Regard t h i s only as an

example.

Change

them as you l i ke . The next

screen

( we

wi l l discuss t h i s express ion

in the next subchapter ) , conta ins the

def in i t i ons

for

the un i t s of measurement

while

the

fol lowing

screen conta ins the

def in i t i ons for the ca lo r i e s .

16


23/132

Fig 3-4 Weightwatcher .

SCR

125

o

1

2

3

4

5

6

7

8

9

( AFB WEIGHTWATCHER ef

( UNIT GLAS : BEER, APPLEJUICE

COCA-COLA, CHAMPAGNE

UNIT SLICE

BREAD

UNIT PIECE

CAKE, MUFFINS

UNIT OZ : BEEF , HAM CHIPS,

NUTS

, CHEESE

10

11

12

13

14

15

UNIT CUP :

RICE,

PASTA

UNIT TBSP [ TABLESPOON

BUTTER ,

UNIT

PKG

:

SEAFOOD

,

SCR

126

o

AFB

WEIGHTWATCHER

ntd

ef

1 MEASUREMENT UNITS )

2 GLAS DROP

+ ;

3 GLASSES

+ ;

4

SLICE DROP +

5 SLICES

+

6 PIECE DROP

+

7

PIECES

+

8

OZ

DROP + ;

9 OZES + ;

10

OF

;

11 START 0 ;

12 TBSP DROP

+ ; :

TBSPS

+

13 PKG

DROP + ;

PKGS

+

14

CUP

DROP + ; : CUPS +

15

17


24/132

SCR 127

o AFB WEIGHTWATCHER cntd ef

1

CALORIES

2

BEER

255

; :

COCA COLA 88

3

BREAD 100

;

4

BUTTER 100

; :

BROWNIES 224

5 RICE

200

; :

GOUDA 108

;

6 MUFFINS 118

7

LASAGNE

241 RAVIOLI 210

8 BURITO 47 ; CNCHIPS 166

9

PEANUTS

179

PTCHIPS

156

10

11

12 AMOUNT DUP

13

14

15

START OK

COCA COLA

1

GLAS O

BREAD

2

SLICES OK

MUFFINS 2 PIECES O

GOUDA

2

OZ.ES OK

BUTTER

1 TBSP

OK

AMOUNT 840

OK

CNCHIPS 2

OZES

O

AMOUNT 1172 OK

LASAGNE 2 CUPS

O

AMOUNT 1654 OK

Fig

3-4

Weightwatcher .

I f you en te r the word BEER , the number 255

i s

put

on

the

s tack

. When you now

enter

2

GLASSES ,

f i r s t

the

number

2

i s

put

onto

the s tack

then

the both top

numbers

( 255

2 ) are mul t ip l ied and the r e su l t i s

added

to

the

previous amount .

To s t a r t t h i s ca lcu la t ion

of

ca lo r i e s you

have to enter the

word

START, which puts a

o on

top

of the

s tack .

The

word

AMOUNT

dupl ica tes

the

top

of

s tack

and

pr in t s

t

on

the screen .

8


25/132

3-6 THE SCREEN.

The

wri t ing

of a FORTH program

can

be done

in

two

ways.

You

can

en te r

t he

FORTH

words

d i r ec t i n to the d ic t ionary or

use

a t ex t

ed i to r

and wr i t e the words i n to a sc reen .

Fiq . 3-5

shows

an example of a sc reen .

FORTH vers ions running on an ATARI use a

screen

wi th

16 l i n e s and 32

charac te r s

each.

SCR

148

o

(SCRN PRINT

10/14/82

ef)

1 0

VARIABLE ROW

0

VARIABLE COLN

2

?FIN -f)

COLN @ 24 = ;

3

lROW

40 0 DO

ROW @

C 32

+

4

DUP

128

> IF

32 -

THEN

5 OUTCHR 1 ROW

+

LOOP

6

7 .SCRN

88

@

ROW

0 COLN

8

BEGIN lROW CRR

1

COLN +

?FIN

9

UNTIL;

10

11

12

13

14

15 -->

Fig 3-5 Textsc reen .

This

uses

512

bytes

of

memory.

Thus,

when

using a disk dr ive , you

can

s t o r e

164

sc reens .

In

t h i s bookle t we

d o n t

descr ibe

the ed i t o r . I t has numerous va r i a t i ons

in

the

var ious FORTH ver s ions .

Please

r e f e r

to the

i n s t r uc t i on

manual

of your FORTH.

Once

you

LO D

it.

have

LO D

wri t t en

compiles

a sc reen ,

you

can

the

words

of

a

19


26/132

screen

i n to the d ic t iona ry .

You

LIST a sc reen . LIST disp lays the

of a

disk screen

on the TV sc reen .

The d e f i n i t i o n s are :

may a l so

conten t

LO D ( n )

LIST ( n )

Compile

disk

screen n

i n to the d ic t iona ry .

L i s t disk screen n on

the TV screen .

There

are

some

convent ions

in the wr i t ing

of a

sc reen . The

f i r s t

l i n e

should

be

a

comment,

not ing the t ask ,

the da te and

the

programmer .

For example :

WEIGHTW TCHER

10/16/82

ef)

The comment in

FORTH

s t a r t s

with

the

opening bracke t and

ends with

the c los ing

bracke t . The i s a FORTH word and must

the re fo re

be fol lowed

by

one space .

Beginning of a comment.

You can use the word INDEX to d isp lay a l l

f i r s t l i n e s of a

disk screen

on the TV

sc reen .

INDEX nn ) Display

the

f i r s t

l i nes

from

screen n to

screen

n .

In

wri t ing a screen , every new d e f i n i t i o n

of a

word

should s t a r t in a new l i ne .

This

makes t eas i e r to

read

a FORTH

program.

After wri t ing you

save

the screen

on

disk

with

the word

FLUSH.

FLUSH

Saves

screen

on

disk

.

20


27/132

3-7 CONSTANTS AND

VARIABLES.

Most

of the

da ta

used for

ca l cu l a t i on

i s

s tored on the s t ack . Sometimes t i s

necessary

to

use

a

cons tan t

or

a

var i ab l e .

The d e f i n i t i o n s of a cons t an t and a

va r i ab l e are:

CONSTANT NAME n) Crea tes a cons tan t

NAME with the

value

n.

VARIABLE

NAME

n) Crea tes a

va r i ab le

NAME and the

i n i t i a l value n.

There i s a

d i f fe rence in

ca l l i ng a

cons tan t

or

a var i ab l e . Cal l ing a cons tan t

py

name,

the

value

of

the

cons tan t

i s

place on the s tack . Cal l ing

a

va r i ab le by

name,

the

address

of t h i s va r i ab le

i s

placed on the s tack

. In

order to ge t the

value

of

a

var i ab l e you have to

f e tch

t

.

This i s done

by the word @ For

changing

the value of

a

var i ab l e the word

(

s to re

)

i s

used.

@

a-n)

na)

Fetches the

conten t

s tored a t address a .

S to res

n

a t address a .

Both

i n s t r u c t i o n s fe tch and

s t o r e

use 16

b i t

numbers.

For

s to r ing

and

fe tch ing

a

s ing le by te the fo l lowing words are used.

C

a-b)

C

ba)

Fetches a s ing le byte

from

address

a .

Sto r es a

s ing le byte

a t

address

a .

21


28/132

Try t h i s :

o

755

C

4

755

C

3

755

C

The

cursor

w i l l disappear .

The

l e t t e r s

are upside

down.

Rese ts

to

the

normal

mode.

Later

we

w i l l use

these

words to cont ro l

with the co lo r and sound r eg i s t e r s of the

ATARI.

You

can increment the value of

a var i ab le

by

o VARIABLE V

V

@

1

+

V

or you

can

use the word + ( p l u s - s to r e .

+

na)

Add n

to

the conten t

a t address a .

Another word ?

fe tches

the conten t of a

va r i ab l e

and

p r

i n t s

.

?

(

a)

Pr in t s

the conten t

of

address a .

The FORTH system i t s e l f uses severa l

cons tan t s and va r i ab l e s

. We

w i l l use the

va r i ab l e

BASE in

the

fo l lowing

example.

The conten t of

t h i s

va r i ab l e dete rmines

the number base in which ca l cu la t ions

a re

made.

I f

t he

value

of

BASE

i s

10,

a l l

ca l cu la t ions are made in decimal . Changing

t h i s value to 16

,

the ca l cu la t ions are

made in hexadecimal . Y

ou

may use however,

any

other value for

ca l cu l a t i ng in any

other number

base

sys t em. Two words are

def ined to se t a spec i f i c

number base .

DECIMAL

(

Set

number

base

dec imal .


29/132

HEX

Set number base

hexadecimal.

n

example:

We def ine :

BIN 2 B SE ;

TRI 3 B SE ;

.BIN ( n BIN

.TRI ( n TRI

DECIM L ;

DECIM L ;

The word

BIN

s e t s

the

number

base to two

and the word

TRI

to t h ree . The t r i n a r y

system uses

only

the numbers O l a n d 2

for

represen t ing a number.

The

words .BIN and

.TRI

take

a decimal value from the s t ack ,

conver ts t to the b inary or

t r i n a ry num-

ber ,

p r in t s

t

and

swi tches

back

in to

the

decimal

number base . Let

us

conver t

some

numbers.

120

.BIN

1111000

O

140 .TRI

12012

O

The word

.

B SE fe tches

the conten t

of

BASE,

dup l ica tes

t

and

p r i n t s

t in

decimal .

The the value

i s

res tored in

BASE.

: .BASE

B SE

@

DUP DECIM L B SE

, .

,

I f

you

only type B SE

@ .

you

wi l l

always

get the r e su l t 10, regard less in which

number base

you

are .

A cons tan t should s tay a cons tan t . But you

can change the value of a cons tan t

with

the

( t i c k word. The br ings the

address

of

a def in i t i on

on

the

s tack .

, N ME ( - a

Find

the address

of

N ME

in vocabulary .

23


30/132

Example:

10

CONSTANT C OK

C

10 OK

12

I

C

OK

C

12 OK

3-8 COMPARISON.

The

comparison

t akes p lace with

the

two

top

numbers

on

the

s t ack .

They

are

rep laced by the r e su l t

of

the

comparison.

The r e su l t

i s a one

i f the

comparison

was

t r ue or

the r e su l t

i s a zero , i f t h i s

comparison was not t rue .

This

boolean

f l ag

i s

used

by the

con t ro l

words,

descr ibed

in

the next chap te r

, to con t ro l

the f lo

w of a program.

The

words used

for

comparison

are :

(

nn f)

f= l ,

i f n

grea te r

than

n

=

(

nn

- f )

f= l ,

i f n

equal

to

n

0

-n

Retr ieve

number

from

re turn

s t ack .

R

-n

Copy

the

top

of

the

re turn

s tack

to

the

parameter

s t ack .

Same

as

1

Use these words only

within

a colon def

i n i t i on

and outs ide

of loops .

Example:

We

def ine

a

word

2SWAP, which exchanges

the

two top

numbers on the s tack with

the

th i rd and the four th

number.

:

SWAP nnln2n3-n2n3nnl

>R ROT ROT R> ROT ROT ;

The

eva lua t

i on of th i s word

on

the s tack

i s shown

i n F i g

4-3

.

29


36/132

4

3

4

3

2

2

4

2

3

2

1

2

3

2

4

3

1

4

1

2

4

3

1

4

3

) R

ROT

ROT

R

ROT

ROT

Fig

4-3

Evalua t ion of

2SWAP

4-3

IF

ELSE THEN

ENDIF).

This

i s

the f i r s t word t o con t ro l the

flow

of a program.

I t

i s used in the form IF

THEN

or

IF ELSE

THEN. Some

vers ions of FORTH use

ENDIF

ins tead of THEN.

The de f i n i t i ons :

IF f)

THEN

IF f)

ELSE

THEN

Example:

The words between IF

and

THEN

ENDIF)

are

executed

i f

f

i s

non

zero .

The words between IF

and ELSE are

executed

i f f i s non zero .

Otherwise the words

between

ELSE and

THEN

ENDIF)

are

executed.

We

def ine a word COMP which compares

the

two top numbers

on

the

s tack . The

message

EQUAL i s pr in t ed i f both numbers are

equa l . I f no t the message SMALLER

or

BIGGER

i s

pr in ted .

The

de f in i t i on

of

the

word COMP i s shown in

Fig

4-4.

30


37/132

F i r s t

2DUP ( n n - n n n n )

OVER OVER ;

DROP

( nn ' )

DROP DROP

NOTEQUAL

(

f)

IF . BIGGER

ELSE

.

SMALLER

THEN;

COMP

( nn ' )

DUP

= IF

.

EQUAL

DROP ELSE

R

draws

a l i ne from

l e f t to

we

def ine

the

mode 7

and

The

next

word

r igh t .

SCR

140

o

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

AFB GRAPHICS 10/20

ef

START

7 GR. 2 0 0 SETCOLOR ;

R>L

( )

9

9

DO

I

10

2

PLOT

LOOP ;

U>D ( ) 9 10 DO

8

I 3

PLOT

LOOP ;

L >R ) 8 8

DO

I 8 2

PLOT -1

LOOP ;

D>U ( ) 9 7 8 DO 9 I 3

PLOT

-1

LOOP

;

RECT START R>L U>D L>R

D>U

;

Fig 5-2 Lines .

The

next

word

U>D

draws a l i n e down

the

screen

s t a r t ing a t

the

ending

poin t of

the previous l i ne . In

the

same

manner

the

words

R>L and D>U are def ined . They always

s t a r t

a t

the end of the former l i ne . The

l a s t word

RECT combines

these words to

draw

a

rec tangle .

Here

you can see one of the advantages of

FORTH.

Once

you have def ined a word, you

can use

t

with in

other words.

With FORTH

t

i s

also easy to change a program. You

may def in a new word

with

another sequence

of

predef ined

words.

Try t in

t h i s

example.

Rearrange

the

words

in

such

a

37


44/132

manner,

so

t ha t

bot tom

l i n e are

two s ide l i ne s .

the top l i n e and the

drawn

f i r s t and then the

In

t h i s

example,

l i ne

one

of

the

t ex t

screen #140

i s

l e f t blank.

In

developing

t h i s

sc reen

the

words FORGET START

were

i n se r t ed . These

words

were i n se r t ed a f t e r

the f i r s t compi la t ion of the sc reen . This

preven t s

the

s tack of

the

vocabulary from

becoming

too l a rge

thus

r ec iev in ig

the

message word NOT UNIQUE

In the

next program,

we wi l l use the

joys t i ck

to draw l i ne s .

Suppose

the red

but ton

i s in

the upper

l e f t co rne r you

ge t the e igh t values shown in

Fig

5-3 for

the

e igh t d i r ec t ions

of the

j oys t i ck by

reading memory

c e l l

632.

4

4

3

Fig

5-3

Joys t i ck Cont ro l l e r

Movement.

Plug

in

a

j oys t i ck in

game

por t one, then

type

632 C

You

wi l l ge t the values shown in

Fig

5-3 .

The de f in i t i on of the words i s shown in

t ex t screen

116.

We

use two

var i ab le s

X

an

Y. The

word

X

increments

the

value

of

X

by

one.

The word Y i s def ined

as

: Y -1 Y

+

;

38


45/132

because Y counts

pos i t i ve

downward on

the

screen.

The

word STICK expects a

value

on

top

of

the s tack

which

i s

equal

to

the conten t

of

game por t one. Then t

decides

which

var i ab le has to be incremented or decre

mented.

SCR 116

o

(AFB

JOYSTICK 10/18 ef)

1 0

VARIABLE X

0

VARIABLE Y

2

X

X 1 ; : -X 1 X 1

3

Y

-1 Y 1 ; : -Y 1 Y 1 ;

4 STICK ( n)

5 DUP 14 = IF

Y

ELSE

6 DUP 13

= IF

-Y ELSE

7

DUP

7

= IF

X ELSE

8 DUP

11 =

IF -X ELSE

9

DUP

6

=

IF

X Y

ELSE

10

DUP 5

=

IF

X

-Y ELSE

11 DUP 9 = IF -X -Y ELSE

12 DUP 10

=

IF -X Y THEN

13 THEN THEN THEN

THEN

THEN

14 THEN THEN ;

15

SCR 118

o AFB GRAFICS

10/18 ef)

1 START 2 0 0 SETCOLOR 7 GR.

2

10

Y 1

10

X 1 ;

3 NOT ( n-n ) 1 XOR ;

4 PL ( n n ) X @ Y @ 2 PLOT;

5

NPL

( nn ) X @ Y @

0

PLOT;

6 ?STICK 632 C DUP 15

=

NOT

7 IF STICK PL THEN DROP

8 PJOY START PL BEGIN

9 ?STICK ?TERMINAL UNTIL

10 0

GR. ;

11

Fig 5-4

Cont ro l l ing the

j oys t i ck .

39


46/132

The program cont inues in screen 118. The

word START se t s

the

gra f i c mode,

the

background colors

and

the

s t a r t i ng

values

for

X and Y. The word NOT i s

used

to

change

the

r e su l t

of

a

comparison.

I f

a

comparison

i s f u l f i l l e d a one i s on the

s tack .

NOT changes th i s value to zero . I f

a

zero

i s on the

s t ack

NOT

changes t

to

one. With t h i s word the Exclusive

OR

funct ion i s used. This funct ion i s shown

in

Fig

5-5 for one b i t . FORTH

app l ie s t h i s

funct ion

b i t

by

b i t

on

the

two

top

numbers

of

the s tack .

Bi t l

o

o

Bit2

o

o

XOR

1

o

o

Fig 5-5 Exclusive Or

The other

l og ica l funct ions

AND

and

OR are

a l so

implemented.The

def in i t i ons are :

AND

nnl-n2 log ica l AND

b i twise

OR

nnl-n2 log ica l OR

b i twise

XOR

nnl-n2

log ica l

XOR

bi twise

Now we cont inue with the program. The word

PL p lo t s a poin t a t X

and

Y in co lor two.

The word ?STICK

determines

i f the j oys t i ck

i s moved in one of the e igh t d i r ec t ions .

Then a poin t i s p lo t t ed . The word PJOY

combines a l l these

words

to

p l o t l i n e s on

the TV screen .

The word NPL p lo t s the po in t in the color

of the background.

This

erases a po in t on

the TV screen .

We

can i n se r t t h i s word in

?STICK to

move

a poin t ac ross the TV

screen .

40

?STICK

632

C

DUP

15

=

NOT

IF NPL STICK PL THEN DROP


47/132

5-2 PATTERN.

The

program in

Fig

5-6

c rea t e s

a random

pa t t e rn . I t uses a

random

number genera to r .

RND

expects

a

number

n

on

the

s t ack .

A

random

number

between 0 and n- l i s

genera ted .

As a s t a r t i ng value for the

random numbers, we use the conten t of

memory

loca t ion 53770.

In

t h i s memory

loca t ion the re

are c rea ted

random numbers

ins ide the ATARI.

SCR

117

o AFB

RANDOM

PATTERN ef)

1 (RANDOM

GENERATOR

)

2

0 VARIABLE RND

53770

@ RND

3

RANDOM RND

@

31421

*

6972

+

4 DUP RND ;

5 RND (

n-n )

RANDOM U* SWAP

6 DROP;

7 RNDP 7 GR. 2 0 0 SETCOLOR

8 BEGIN 160

RND

80

RND

9 16 RND PLOT

10

?TERMINAL UNTIL ;

11

12

13

14

15

Fig

5-6

Random

Pa t t e rn .

The

word

RNDP se t s

the

gra f i c mode 7 and

the background co lo r .

In

a loop,

terminated by one of the yel low keys,

t

c rea tes random

numbers

for the X Y

coord ina tes

and

the

co lor .

The r e s u l t i s

displayed

on

the

TV

screen

.

41


48/132

5-3

SOUND

AND COLOR

The word

SOUND

uses four

parameters

on the

s t ack .

SOUND nnln2n3)

n (

0-15

)

i s the

volume, n l

a

d i s to r t i on ,

n2 the

frequency and

n4

the channel .

For

crea t ing

severa l

sounds

and

noises ,

we

use the random

number

genera tor and

a

wait

loop. The

word WAIT reques t s

one number

on the s tack . The higher

the

number, the

longer

the

delay. The

t ex t

screens

81

to

85

in

Fig 5-7 conta in

some

sound

words,

such as the word THUNDER in screen 81.

Using

random

pi t ch

and

volume,

a

sound

l ike

a

swarm

of

f l i e s

i s generated .

ENG

uses

in te rmi t t en t sound

for

noise tha t

sounds

l i ke

an

engine.

Fig 5-7 Sound.

42

SCR

081

o

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

AFB SOUND

WAIT

0

DO

C (

n-n

I

SWAP /

10/20 ef

LOOP

;

11 RND

5 + 10

OFF 0 0 0 0 SOUND

o 0 0 1

SOUND

;

T

100

5

DO

I C

8

I 0

SOUND

I C

8

I 20 + 1

SOUND

DUP WAIT

5

RND +LOOP OFF

;

THUNDER

300 T

-->


49/132

SCR

082

o

AFB SOUND cntd

ef

1 FLY)

2

PI

( n) 7

RND

250

+

3 V ( n) 4

RND

6 +

4 F V

14

PI 0 SOUND

5

FLY

BEGIN F 500

WAIT

6 ?TERMINAL UNTIL

OFF

7

ENGINE

8

ENG

BEGIN 10 10

250

0

SOUND

9

1500

WAIT

OFF

?TERMINAL

10 UNTIL

11

12

13

14

15 -->

SCR

083

o

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

AFB

SOUND

cntd

ef

INCR ( n) 10 / 1

DO

I 10 60 0 SOUND

LOOP ;

DECR

( n) 2 10 / DUP 1

SWAP DO DUP

10 60 0

SOUND

-1

+LOOP

DROP ;

T

100

a

DO

I INCR 2

+LOOP

TT

0

100 DO

I DECR -2

+LOOP

CC

0 100 DO I INCR I DECR

-2 +LOOP

-->

43


50/132

SCR 084

o

AFB

SOUND cntd ef)

1 15 VARIABLE VI

15

VARIABLE

V2

2 15 VARIABLE V3

3 ST 15 VI 1 15 V2 1 15 V3 1 ;

4 : SS VI @ 8

20

0 SOUND

5 V2 @ 8 40 2 SOUND

6 V3 @ 8 70 2 SOUND

7

8 DEC

-1

VI 1

-1

V2 1

9 -1

V3

1

;

10

EXPL ST BEGIN SS DEC

11 1000 WAIT V3 @ 0< UNTIL

12

13

14

15

SCR 085

a

AFB SOUND

cntd

ef)

1 SI 15 a DO I 10 60 I 2 -

2 a SOUND 100 WAIT

LOOP

;

3

4

SIREN

BEGIN

SI

OFF

50

WAIT

5 ?TERMINAL UNTIL ;

6

7

8

DWN

200 100 DO 8 10 I

a SOUND

9 100

WAIT LOOP ;

10 UP 100 200

DO

8 10 I 0 SOUND

11 100 WAIT -1 +LOOP ;

12

EUSI

10

0

DO

UP

DWN

LOOP

13

OFF;

14

15

The word CC in sc reen 83 s imula tes a

dropped co in These examples are from the

book

ATARI BASIC

Learning

by

Using

by

Tomas E. Rowley .

44


51/132

Some more

sound words are

in the next

screens

EXPL s imula tes an

explosion

by

changing

the

volume and

the

pi tch

on

three

channels . In the

l a s t

screen

we have

the

word

SIREN

for s imulat ing

an

american

pol ice s i r en and the word EUSI for an

european pol ice

s i r en

The

bes t

way

to crea te

sound

e f fec t s i s

the methode of t r i a l

an e r ro r

Define new

words and combine them in

d i f f e ren t

ways.

SCR

# 086

0 ( AFB

COLOR

10/22

ef

1

CF 712

C@

710

C@

712

C

2

709

C@

710 C 709

C

3

4 CCF 100 0

DO

CF

100

WAIT

5

LOOP 0

GR.

;

6

7

BG

254 0 DO I 712 C

500

WAIT

8 2 +LOOP ;

9

10

FG 254

0

DO

I

710 C

500 ~ v I T

11 2

+LOOP

12

SCR

# 087

o

AFB

COLOR cntd ef

1 DI

16

0

DO

I 709

C

100 WAIT

2

LOOP;

3 AR 0

14 DO

I

709 C

100 WAIT

4 -1

+LOOP

;

5

6 CURS (

nnl

85 84 C

7 CLR 125 EMIT ;

8 DIS CLR

10

5 CURS

9 222 710

C

. HELLO

10

1000 WAIT DI KEY AR ;

11

12

Fig

5-8

Color.

45


52/132

In

the

t ex t screens 86 and 87 ( Fig

5-8

,

the

s to re

and

fe tch

words

are

used

to

change

the

con ten t s of

the

co lo r r eg i s t e r s .

The word CF ro t a t e s the conten ts of the

color

r eg i s t e r s .

This

causes

a

quick

change

of

foreground and

background co lors .

Use t h i s word in a new d e f in i t i o n of

THUNDER

BG

changes the background

color

and

FG changes the foreground color

In

the

next screen, the

t ex t

HELLO

disappears

and,

a f t e r

press ing

a key,

t

reappears .

The

word

DIS

uses

two

other

words CLR and CURS.

The word

CURS reques ts

two

numbers on the

s tack . N

i s the

hor izonta l row and

n l

the v e r t i c a l column.

By sending out an end of

f i l e

charac te r (

155 EMIT ) the cursor i s placed a t the

spec i f i ed

pos i t i on .

The word CLR

c l ea r s

the TV

sc reen

and pos i t ions

the

cursor

in

the

upper

l e f t

corner .

5-4

H E X U M ~

Most

of the FORTH vers ions have def ined

the

word DUMP

as

t h a t

which dumps

the

conten t

of

memory

loca t Ions

on

the

screen .

The program

in

Fig

5-9

(

screens

88

and

89

) i s a s imi la r program. The word

DDUMP

reques ts

two

numbers on the s t ack . N i s

the

s t a r t i n g

address

and nl

the

number

of

l i nes ,

e igh t

bytes each.

SCR

088

0

( AFB

HEXDUMP

10/22

ef

1

HEX

2

LNE ( n DUP DUP 8 SWAP

3

DO

I

C

3

.R LOOP

.

4 NR

CR CR

5 SPACES 8 0

5

DO

I 3

.R LOOP CR

6

DOT

DROP 2E ;

46


53/132

7

8 ATARI (

n-n

DUP

20

IF

DOT THEN

13

THEN THEN

THEN THEN

THEN

;

14

15 -->

SCR

089

o AFB

HEXDUMP cntd

ef

1 ASCII ( a-a DUP DUP 8

2 SWAP DO I

C

ATARI

EMIT

3 2 SPACES LOOP ;

4

5

6

7

8 HDUMP ( n-n ) CR

DUP

SPACE

9 LNE

CR

7 SPACES ASCII 8

;

10

DDUMP (

an

HEX

11

NR

0

DO

HDUMP

LOOP DROP

12

DECIMAL

13

DECIMAL

14

15

Fig

5-9 Hexdump.

An example of

the

pr in tou t i s shown in Fig

5-10.

47


54/132

HEX

3008

9 DDUMP

0 1

2 3

4

5 6

7

3008

86

4B

45

59

4C

49

D4 EA

f

K

E Y L

I T

j

3010

2F D9

C 60

D F3 2F 7C

y

s

I

3018

C 60

D El

8 lC

C 3D

a

=

3020 C

FA

8 F3 2F

70 D 9C

z

s

P

3028

B

9C

B

91

C

9

F 59

q

Y

3030 8 4

0

22

B

FA 8 7A

z z

3038

8 E4 FF F B

31 0 87

d

1 g

3040

43 4F

4E 54 52

4F

CC 8

C

0

N

T R

0

L

3048

30

SF 11

13

20 86

C

46

0 f

F OK

Fig 5-10

Hexdump

Pr in tou t .

The word ATARI changes

a l l unwanted

charac te r s

for example

the

byte 9B which

erases the screen

to

do ts .

This word i s

used with in the

word

ASCII, which

p r in t s

the

ASCII

charac te r s .

LNE pr in t s one l i n e

of hex

bytes

while NR does

the

numbering

on top of the pr in tou t .

Next

we

look

a t some mathematical

examples.

5-5 LARGEST

COMMON

DIVISOR

We

use the

a lgor i thm

of

ca l cu l a t e

the

l a rges t

common

two numbers A

and B. F i r s t the

48

EUCLID

to

d iv i so r

of

remainder


55/132

of

lB

i s

determined by

A B MOD

I f

the

remainder

R

i s zero

B

i s

the l a rge s t

common

d iv i so r . I f

R i s not zero A i s s e t

to

Band

B

i s s e t

to

R

and

the

modulo

d iv i s ion

i s repea ted un t i l

R i s zero . The

def in i t i on of

LCD

i s shown in

Fig

5-11.

0

AFB

MATH

EXAMPLES

ef

1

2

LCD

BEGIN SWAP OVER

MOD

DUP

3

0= UNTIL

DROP

;

4

27

21

LCD

3

OK

Fig

5-11

Larges t

Common

Divisor .

STACK

27

27

2

2 27

2

2

6

2

6

2

6

6

2

6

6

3

6 3

6

3

3

6

3

3

0

3

0

3

TOS

27

2

2

27

2

6

6

0

6

2

6

3

3

0

3

6

3

0

0

1

0

3

INPUT

27

2

BEGIN

SW P

OVER

MOD

DUP

0=

UNTIL

SW P

OVER

MOD

DUP

0=

UNTIL

SWAP

OVER

MOD

DUP

0=

UNTIL

DROP

Fig

5-12

Larges t

Common

Divisor

Evalua t ion on the s tack

49


56/132

For a b e t t e r unders tanding of t h i s

d e f in i t i o n

the

evalua t ion on

the

s tack

for the

given

example i s

shown

in Fig 5-12.

5-6

FIBBOCONACCI

NUMBERS

Fibboconacci numbers are a

se r i e s

of

numbers. The

next

element of t h i s se r i e s

i s always

the

sum of the

two predecessors .

The se r i e s

s t a r t s

with

zero

and

one.

The

word

FIB

in Fig 5-13

c rea t e s these

numbers.

This i s

an example for

the BEGIN

WHILE

REPEAT loop. FIB

expects

on the

s tack one

number

which determines the

end

of the

s e r i e s .

I f the ca lcu la t ed

element i s

l a rge r than t h i s

number,

the ca l cu la t ion

s tops .

SCR 099

a

1

2

3

4

5

6

AFB

MATH

EXAMPLES

cndt

ef

FIB (

n

CR

a

1 BEGIN DUP

>R

ROT

DUP

R>

> WHILE

ROT ROT

DUP

ROT +

DUP

REPEAT DROP DROP DROP

100 FIB

1 2 3 5 8 13 21 34 55 89 144 OK

Fig

5-13 FIBBOCONACCI Numbers. (

The

evalua t ion on

the

s tack for

the

f i r s t

t h ree loops i s

shown

in

Fig 5-14.

50


57/132

20

20

20

2

1

2 1

2 1

1

2 1

1

20

1

20

20

1 2

2

1

1

2

1

1

20

1

20

2

1

2

1

1

2

1

1

2

1 1

2

1 1

1

20

1

1

2 1

1

20

1 1

1

2

1

1

1

1 20

1 1 2

20

1 1

2

20

1

1

1

20

1

1

1

20

1

20

1

20

1 1

20

1 1

1

20 1

1

1

2

1

2

2

1

2

2

2

1 2

20

1 2

20

1 2 2

Fig 5 14 FIBBOCON CCI

Numbers.

Evaluation

on

the

stack.

2

FIB

o

BEGIN

UP

R

R T

UP

R

WHILE

R T

R T

UP

R T

+

UP

REPE T

UP

R

R T

UP

R

>

WHILE

R T

R T

UP

R T

+

UP

REPE T

UP

5


58/132

5-7 PRIME NUMBERS.

In the

next

example, we ca lcu la t e the

prime numbers between two

l imi t s .

The

algor i thm

used

i s very

s imple .

The word

PTEST t e s t s

within

a

loop,

i a

number

i s

d iv i s ib l e by

the loop

index.

The loop

s t a r t s with two

and ends

a t ha l f

of

the

number. In t h i s program the

predef ined

word LEAVE i s

used.

This word t e rmina tes

the execut ion

of

a loop.

The

program

cont inues

a f t e r

the

next LOOP

word.

LEAVE

Terminates a

loop

I f TEST f inds a remainder equal

to zero ,

a

zero i s

placed

on the

s tack

- and the loop

i s

l e f t .

The

program then

cont inues

with

the

word

DUP.

With

a

zero

on

the s tack

the

word . PRIM i s

not

executed

and

the top of

s tack

i s discarded . To format the output

a

var iab le

ROW i s used.

The program

i s

shown

in

Fig 5-15.

52

SCR

100

o

2

3

4

5

6

7

8

9

10

11

12

13

14

15

AFB

MATH

EXAMPLES cnd t

ef)

4 VARIABLE

ROW

TEST ( n-f) MO 0= ,

.PRIM ( n-n) DUP 4

.R ROW @

DUP 0= IF

CR DROP

4 ELSE

1 - THEN #ROW ;

PTEST

n ) DUP

2 / 2

DO

DUP

I TEST

IF

0

LEAVE

THEN

LOOP

DUP IF .PRIM ELSE DROP

THEN

DROP ;

PRIM (

nn' ) CR

4

ROW

DO I PTEST LOOP CR


59/132

200 1

PRIM

1 3

5

7

11

13 17 19 23

29

31

37 41 43

47

53 59

61

67

71

73

79 83

89

97

101

103 107 109

113

127

131

137 139

149

151

157

163

167 173

179

181 191

193

197

199

OK

Fig

5-15

Prime Numbers.

5-8 HORE

SOUND

AND

GRAFICS.

I found some new sounds

in the

September

i ssue

of

COMPUTE

magazine.

I

t r ns l t ed

these examples from BASIC to FORTH. These

new sound

words re shown

in Fig 5-16.

There

i s

another thunder

which

you can

combine with

the

old thunder and r in to

cre t e stormy weather .

SCR 094

0

MORE

SOUND 10/26

ef

1

B

(

-n

255

RND#

50

+

2

X

( -n

200 RND#

;

3

Tl

(

)

B 1 DO

15

8

I 0

SOUND

4

LOOP ;

5 T2

( )

X 1 DO LOOP ;

6

TH

)

2 0

DO

Tl OFF

7

T2 OFF

LOOP

;

8

STO

TH

TH THUNDER

TH ;

9

Rl

n)

o 0 2 SOUND ;

10

RAIN

150

0 DO I 10 / Rl

11

100 WAIT 2 +LOOP BEGIN

12

?TERMINAL UNTIL ;

13

14

15

53


60/132

o MORE SOUND

cntd

ef)

1 :

HB

10 1

DO

15 3

12

0 SOUND

2

1000

WAIT OFF 6000

WAIT

LOOP

3

4

-1 VARIABLE XX

5 LOI 40

150

DO I 10 / 0 15 0

6 SOUND XX @ LOOP

7 LO SO lDO LOI XX @

-7

>

IF

8

-1 XX 1 THEN LOOP

9 LS

10

10

40

1 SOUND

10

8 10

10

2 SOUND

11

10

10 90

3

SOUND

12

STE

2

0 DO LS

4000

WAIT

XSND

13 1000 WAIT LOOP

14 STEAM -1 XX 1 LO STE LO

15

XSND

Fig 5-16

More

sound.

The

program

in

Fig

5-17

produces

the

gra f i c

shown in p ic tu re 5-18. The l i nes

are

drawn in gra f i c mode

e igh t

Draw t h i s

p ic tu re as

t

i s and then a second t ime

with the background co lo r I t appears and

d isappear s

o

MORE

GRAFICS 10/26

ef)

1 0

VARIABLE X

0

VARIABLE Y

2

CG

8 GR 0 0 2 SETCOLOR

3 SG 260 X

10

Y

4

PG

160 80 1 PLOT

5 -X -10 X

1

6

X 10 X 1

7 -Y -10 Y 1

8

Y

10

Y

1

9 LG X @ Y @ 1 DRAWTO

10

LL

20

0 DO PG LG

-X

LOOP

11 DD

15 0

DO PG

LG Y

LOOP

12 RR 20 0 DO PG LG X LOOP

13 UU

15 0 DO PG LG -Y LOOP

14 PIC

CG SG LL DD RR UU

15

Fig 5-17 Rayshaped pa t t e rn

54


61/132

Fig

5 18

Pic tu re of the

rayshaped

pa t t e rn .

5 9

USING THE

G ME PORTS FOR CONTROL

APPLICATIONS .

The ATARI uses

two

6520 Per iphera l

In te r face Adapters P IA

)

for the

game

por t s . These

por t s can

be

used

to

t ransmi t

or

to recieve data . The

6520

provides two

b i -d i r ec t i ona l

por t s

, A and i two cont ro l

r eg i s t e r s

and

four

in te r rup t

l i ne s .

In

our

examples we only use the por t s and the

con t ro l r eg i s t e r s

. The four r eg i s t e r s have

the

fo l lowing

addresses :

PORT

=

D300

PORTB

=

D301

P CTL

=

D302

and PBCTL

=

D303

55


62/132

The data d i rec t ion for the

two

por t s i s

se t by two

data

di rec t ion r eg i s t e r s DDRA

and DDRB. Both,

the

por ts and

the

data d i r -

ec t ion

r eg i s t e r s

have the same

addresses .

Bit two of

the

cont ro l r eg i s t e r determines

which

one of the

two r eg i s t e r s

i s

accessed.

I f

b i t two of

the

cont ro l r eg i s t e r PACTL

i s

one,

PORTA ac t s as a

por t .

I f b i t two

i s zero,

PORTA

ac t s as a data

d i r ec t ion

r eg i s t e r .

A l i ne

of

a

por t

i s

s e t

to

an

output

i f

the

corresponding

b i t

in the

data d i rec t ion

reg i s t e r

i s

se t to

one.

Respect iv ly a zero marks a l i ne as inpu t .

The

word

INIT in Fig 5-19 se t s the four

lower b i t s

of

por t A as outpu ts .

These

four l i nes

are avai lable

a t

game por t

1 .

SCR

#

104

o

AFB

PORT CONTROL 10/16

ef)

1 HEX D300 CONSTANT

PORTA

2

D30l

CONSTANT PORTB

3 D302 CONSTANT PACTL

4 D303 CONSTANT PBCTL

5

INIT

30

PACTL

C

6 OF PORTA C

7

34

PACTL C

8 00 PORTA C

9

10 DECIMAL

11

12

PAl (

b)

PORTA

C ;

13 WAIT ( n) 0 DO

LOOP

14

15

Fig 5-19

I n i t i a l i s a t i on

of the por t s .

We

use

the

c i r cu i t

shown

in

Fig

5-20

to

demonstra te the output of data .

56


63/132

0 0

6

89

GAME

CONNECTOR

I

I

INSIDE ATARI

22 I

~

001

l

I

I

I

1

=

PAD

2

=

PA

3

=

PA2

4 = PA3

7 =GND

8 =

vee

REPEAT 4 TIMES

NPN

TRANSISTOR

VCC

= 5V

Fig 5 20

Schematic of

the c i r c u i t

Fig

5 21

The exper imenter board .

57


64/132

Fig

5-21

The

experimenter

board.

Screen 105 in Fig 5- 22 conta ins th ree

programs.

RL s imula tes

a

running l i gh t

The

four

LED s

turn on and

of f

one a f t e r the

other

The

sequence

s t a r t s

with

one

on

the

s t ack

This tu rns

on

LE one.

The

second LE i s

turned on by mult iplying the top of the

s tack

with

two. With an addi t ional

mul t ip l i ca t ion the th i rd LE i s switched

on.

The l a s t

LE

i s turned on with the

number

eight

on

the s t ack I f

the number

on

top

of

the

s tack

i s

equal to 16 the

sequence r e s t a r t s

with

one.

58


65/132

SCR

105

o FB

PORT

CONTROL cn td ef

1 RL 1 BEGIN DUP P L 2

DUP

2

16

=

IF

DROP

1

THEN

2000

WAIT

3

?TERMINAL UNTIL

4

5

LB

0 BEGIN DUP

P L

2 1 +

6 DUP 31 = IF DROP a THEN

7

1000

WAIT ?TERMINAL UNTIL

8

9

OINIT

INIT

0 DUP

P L

10 NEW 1 SW P DUP 1

=

IF

DROP

11 ELSE 1 DO 2 LOOP THEN

12

ON

( n) NEW

OR

DUP

P L

13 OFF (

n)

NEW

XOR

DUP

14

P L

15

Fig

5-22

Running

l i g h t ,

l i g h t b a r

and

ON

OFF

LB s imu la te s a l i g h t b a r . The

LED s

are

tu rned of f u n t i l

a l l

four LED s

are

The

sequence s t a r t s with one.

mul t ip ly ing with

two

and -

adding one

we

t h r ee .

This

value

tu rns

on

LED

one

and

not

on.

By

ge t

two.

n add i t i ona l m u l t i p l i c a t i o n

and

add i t i on

l eaves t he value seven on top of the s t ack .

This

t u r n s

on

LED

one, two and t h r ee .

After

a l l

LED s a re tu rned on a zero on

top of the s tack

tu rns

a l l

o f f .

Both

programs

use

t he

WAIT

loop .

The

words def ined in sc reen 105, l i n e 9

th ru 14, can be used to tu rn on or

of f a

p a r t i cu l a r LED.

1 ON t u rn s on

LED one,

3

ON

t u r n s on

LED

t h r ee

and

1 OFF

t u r n s

o f f

LED

one.

59


66/132

The word OINIT i n i t i a l i s e s p o r t A, p laces

a zero

on t op of

the

s tack and t u rns

of f

a l l

LED s.

The

word

NEW

de te rmines which

LED has

to be t u rned

on.

The

s t a t e

of

the

four

LED s

i s

s to red

in

the

four

lower

b i t s

of

a byte

on

top of the s t ack . A

one

markes the corresponding LED as turned on,

a

zero

marks

t as turned

of f . Using

the

l og ica l OR

func t ion the new

LED

i s added.

In the

same

way a LED i s turned of f using

the l og ica l XOR

func t ion .

The app l i ca t i on

in

Fig

5-23

s imula t es a

dice .

Seven LED s are grouped

to form

the

spo t s of a dice see Fig 5-25 . The word

DINIT

i n i t i a l i s e s por t A.

Seven

l i ne s

are

used as outpu t , one l i n e as an inpu t .

A

pushbut ton i s connected to

t h i s

l i n e see

Fig 5-24) The word PA

f e t ches

the

con ten t

of

por t

A

and

masks

out

the

seven

low

order

b i t s . 128 AND). With

128 XOR

b i t e igh t i s inver ted . The number 128 i s

read i f t he but ton

i s

pressed and a

zero

i s

read

i f t i s not pressed . The next

words ID th ru 6D

r e l a t e

the

decimal

numbers

1 t h ru 6

to

the s ix

spo t s of

the

dice .

These

words

use

a

binary

p a t t e rn .

For

i n s t ance

0001000

tu rns

on

the LED in

the middle . This i s equal to a

throw

of

one.

OD

i s used as a dummy

d e f i n i t i o n

in

the CASE: s ta tement CDICE.

60


67/132

SCR #

106

o

(AFB

PORI CONI ROL cntd

ef)

1

HEX

2 DINIT

30

PACl L

C

3

7F PORI A

C

4

34 PACl L

C

5

00

PORI A

C

6

DECIMAL

7

PA

(

-b

roRI'A C 128

ND

8 128

XOR

; 2

BASE

9 ID

0001000

PAL

;

10

2D

1000001 PAL

11

3D

0101010

PAL

;

12

4D

1010101 PAL ;

13 5D 1011101

PAL

14 6D 1110111

PAl

DECIMAL

15 OD

; -

SCR

#

107

o (AFB roRI CONI ROL cntd

ef)

1 CASE:

CDICE

OD

ID 2D 3D

2

4D 5D

6D

;

3

BU ITON

1 BffiIN

DROP

PA@ DUP

4

UNTIL

500 WAIT

5 BffiIN

WHITLE PA

6 REPEAT;

7 DICE 1 BffiIN

1 + DUP

7

=

8

IF

DROP

1

THEN DUP

CDICE

9 PA UNTIL

500

WAIT

1

10

BffiIN

WHILE

PA

REPEAT

11 DROP;

12

DODI

BffiIN BUTTON DICE

13 1000

WAIT

?TERMlNAL

UNTIL

;

14

15

Fig

5-23

S imu l a t i ng

a

d i c e

61


68/132

The word

BUTTON

wai t s in the BEGIN . UNTIL

loop un t i l

the but ton

i s

pressed.

Then

a delay loop

fol lows to

suppress the

bouncing

of

the key. The BEGIN

WHILE

UNTIL

loop

i s

l e f t

on

re leas ing

the but ton .

The

word

DICE

s t a r t s

the count . Press ing

the

but ton

s tops it and the thrown number

i s shown

on

the disp lay .

62

. . ; t l ) C D I '


69/132

Fig

5 25

The

dice

63


70/132

Text and strings

6.

TEXT ND STRINGS.

In

the

s tandard vers ion

of FORTH, the re

are no s t r ings or s t r i ng funct ions

implemented.

Yet

t

i s

very

easy

to

en ter

t ex t or to pr in t out

t ex t .

6-1 INPUT/OUTPUT OF TEXT.

The word EXPECT expects

the input of

cha rac te r s .

The def in i t ion

i s :

EXPECT

a n ) Expects n charac te r s

For

the

specia l

address

the

top

of t ex t a t address

a .

Also

te rminated by CR.

input of

t ex t you can

use a

area in memory

ca l l ed

PAD. The

of

P D

i s

always

68 bytes

beyond

of

the vocabulary s t ack .

P D

- a )

Address of

P D

i s put

on

the s tack .

Example:

P D 15 EXPECT RET THIS

IS

FORTH RET

6


71/132

The t ex t THIS IS FORTH i s s tored in

To

get the

momentary

address

of PAD

PAD and t ry to ge t the t ex t out onto

screen with DUMP

or

DDUMP You

can

use the

predef ined

word

TYPE.

PAD.

type

the

also

TYPE a n )

Pr in t s

n charac te r s

of

t ex t , s t a r t i ng a t

address a .

I f we

have s to red

t ex t as in

the example

above

and

made

no

new

de f in i t i ons ,

which

would a l t e r the address of the top of the

vocabulary s tack , we

can

get the t ex t from

PAD with:

PAD

15 TYPE

RET

THIS IS FORTH

We can

make

a pr in tou t

of

only a par t of

the

t ex t .

We

are

able

to

change

the

s t a r t -

ing address and the number of cha rac te r s .

PAD 2 + 2

TYPE

p r i n t s

IS.

We

use

a new word, TEXT, to read t ex t

i n to

PAD.

In

some vers ions TEXT

i s

a predef ined

word.

The def in i t ion i s :

TEXT c

PAD 72 32 FILL WORD

HERE

COUNT

PAD SWAP CMOVE ;

F i r s t ,

we

must descr ibe

severa l

new words

used in t h i s def in i t ion . The word FILL

f i l l s

memory

ce l l s

withe

the

byte

b .

FILL

a n b )

F i l l

n bytes , s t a r t i ng

a t

address

a , with the

byte

b .

The next new

word

i s

WORD

There are

two

d i f f e r en t def in i t ions

of WORD in FIG FORTH

and

in FORTH-79.

65


72/132

WORD

c ) Read t ex t from

the

input buf fe r u n t i l

the

de l imi te r c

i s encoun-

t e r ed . FIG FORTH

WORD

c - a n )

Read t ex t

from

the

input buf fe r ,

un t i l

de l imi te r c

i s encoun-

t e red . Leave

the

address

a and

the

l ength n of

the

t ex t

on

the

s t ack .

FORTH-

9

Documents

FORTH on the Atari Learning by Using