Microprocessor System Design

Outline

• Address decoding

• Chip select

• Memory configurations

Minimum Mode

MEMORY

D7 - D0

A19 - A0

RD

WR

SimplifiedDrawing of

8088 MinimumMode

D7 - D0

A19 - A0

MEMR

MEMW

When Memory is selected?

Minimum Mode

MEMORY

D7 - D0

A19 - A0

RD

WR

SimplifiedDrawing of

8088 MinimumMode

D7 - D0

A19 - A0

MEMR

MEMWCS

220 bytes or 1MB

What are the memory locations of a 1MB (220 bytes) Memory?

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

Example: 34FD0 0011 0100 11111 1101 0000

Interfacing a 1MB Memory to the 8088 Microprocessor

2300000

00001

10000

10001

10002

10003

10004

10005

10006

10007

10008

95

::

45

98

27

39

42

88

07

F4

8A

::

20020

20021

20022

20023

FFFFD

FFFFE

FFFFF

29

12

7D

13

19

25

36

::

A19

A0

:

D7

D0

:

RD

WR

A19

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

CS

Instead of Interfacing 1MB, what will happen if you interface a 512KB Memory?

What are the memory locations of a 512KB (219 bytes) Memory?

A18 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

Interfacing a 512KB Memory to the 8088 Microprocessor

A18

A0

:

D7

D0

:

MEMR

MEMWXXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

2300000

00001 95

::

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

::

A18

A0

:

D7

D0

:

RD

WR

CS

A19What do we do with A19?

What if you want to read physical address A0023?

A18

A0

:

D7

D0

:

MEMR

MEMWXXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

A000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

2300000

00001 95

::

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

::

A18

A0

:

D7

D0

:

RD

WR

CS

A19

What if you want to read physical address A0023?

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

A0023 1010 0000 0000 0010 0011

A19 is not connected to the memory so even if the 8088 microprocessor outputs a logic “1”, the memory cannot “see” this.

What if you want to read physical address 20023?

A18 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

20023 0010 0000 0000 0010 0011

For memory it is the same as previous one.

Interfacing two 512KB Memory to the 8088 Microprocessor

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

9700000

00001 D4

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

A3

92

45

33

2C

98

12

:

A18

A0

:

D7

D0

:

RD

WR

CS

• Problem: Bus Conflict. The two memory chips will provide data at the same time when microprocessor performs a memory read.

• Solution: Use address line A19 as an “arbiter”. If A19 outputs a logic “1” the upper memory is enabled (and the lower memory is disabled) and vice-versa.

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

9700000

00001 D4

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

A3

92

45

33

2C

98

12

:

A18

A0

:

D7

D0

:

RD

WR

CS

What are the memory locations of two consecutive 512KB (219 bytes) Memory?

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

9700000

00001 D4

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

A3

92

45

33

2C

98

12

:

A18

A0

:

D7

D0

:

RD

WR

CS

When the P outputs an address between 80000 to FFFFF, this memory is selected

When the P outputs an address between 00000 to 7FFFF, this memory is selected

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

9700000

00001 D4

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

A3

92

45

33

2C

98

12

:

A18

A0

:

D7

D0

:

RD

WR

CS

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

9700000

00001 D4

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

A3

92

45

33

2C

98

12

:

A18

A0

:

D7

D0

:

RD

WR

CS

A18

A0

:

D7

D0

:

RD

WR

A19

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

9700000

00001 D4

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

A3

92

45

33

2C

98

12

:

A18

A0

:

D7

D0

:

RD

WR

CS

What if we remove the lower memory?

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CSWhen the P outputs an address between 80000 to FFFFF, this memory is selected

When the P outputs an address between 00000 to 7FFFF, no memory chip is selected !

Full and Partial Decoding

• Full Decoding– When all of the “useful” address lines are connected the

memory/device to perform selection

• Partial Decoding– When some of the “useful” address lines are connected

the memory/device to perform selection

– Using this type of decoding results into roll-over addresses

Full Decoding

A18

A0

:

D7

D0

:

MEMR

MEMW

XXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

A19

2300000

00001 95

:

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

:

A18

A0

:

D7

D0

:

RD

WR

CS

Full Decoding

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

A19 should be a logic “1” for the memory chip to be enabled

Full Decoding

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

Therefore if the microprocessor outputs an address between 00000 to 7FFFF, whose A19 is a logic “0”, the memory chip will not be selected

Partial Decoding

A18

A0

:

D7

D0

:

MEMR

MEMWXXXX

BP

ES

DS

SS

CX

BX

AX

XXXX

2000

0000

0023

3F1C

FCA1

SP

DX

XXXX

CS

SI

XXXX

XXXXIP

XXXXDI

2300000

00001 95

::

20020

20021

20022

20023

7FFFD

7FFFE

7FFFF

29

12

7D

13

19

25

36

::

A18

A0

:

D7

D0

:

RD

WR

CS

A19

Partial Decoding

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

The value of A19 is INSIGNIFICANT to the memory chip, therefore A19 has no bearing whether the memory chip will be enabled or not

Partial Decoding

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

ACTUAL ADDRESS

Partial Decoding

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

00000 0000 0000 0000 0000 0000

7FFFF 0111 1111 1111 1111 1111

80000 1000 0000 0000 0000 0000

FFFFF 1111 1111 1111 1111 1111

ACTUAL ADDRESS

Interfacing two 512K Memory Chips to the 8088 Microprocessor

8088Minimum

Mode

A18

A0

:

D7

D0

:

MEMR

MEMW

A19

512KB#2

A18

A0

:

D7

D0

:

RD

WR

CS

512KB#1

A18

A0

:

D7

D0

:

RD

WR

CS

Interfacing one 512K Memory Chips to the 8088 Microprocessor

8088Minimum

Mode

A18

A0

:

D7

D0

:

MEMR

MEMW

A19

512KB

A18

A0

:

D7

D0

:

RD

WR

CS

Interfacing one 512K Memory Chips to the 8088 Microprocessor (version 2)

8088Minimum

Mode

A18

A0

:

D7

D0

:

MEMR

MEMW

A19

512KB

A18

A0

:

D7

D0

:

RD

WR

CS

Interfacing one 512K Memory Chips to the 8088 Microprocessor (version 3)

8088Minimum

Mode

A18

A0

:

D7

D0

:

MEMR

MEMW

A19

512KB

A18

A0

:

D7

D0

:

RD

WR

CS

Interfacing four 256K Memory Chips to the 8088 Microprocessor

8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS

8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS

Memory chip#__ is mapped to:

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

----- ---- ---- ---- ---- ----

8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS

8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CS

8088Minimum

Mode

A17

A0:

D7

D0:

MEMRMEMW

A18

256KB#3

A17

A0:

D7

D0:

RDWR

CS

A19

256KB#2

A17

A0:

D7

D0:

RDWR

CS

256KB#1

A17

A0:

D7

D0:

RDWR

CS

256KB#4

A17

A0:

D7

D0:

RDWR

CSI1I0

O3

O2

O1

O0

Interfacing several 8K Memory Chips to the 8088 P

8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#?

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::

8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#128

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::

Interfacing 1288K Memory Chips to the 8088 P

8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#128

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::

Memory chip#__ is mapped to:

A19 to A0

(HEX)

AAAA

1111

9876

AAAA

1111

5432

AAAA

1198

1000

AAAA

7654

AAAA

3210

----- ---- ---- ---- ---- ----

Memory Terms

• Capacity – Kbit, Mbit, Gbit

• Organization– Address lines

– Data lines

• Speed / Timing– Access time

• Write ability– ROM

– RAM

ROM Variations

• Mask Rom

• PROM – OTP

• EPROM – UV_EPROM

• EEPROM

• Flash memory

RAM Variations

• SRAM

• DRAM

• NV-RAM

– SRAM – CMOS

– Internal lithium battery

– Control circuitry to monitor Vcc

Memory Chip

• 8K SRAM

• to be specific:– 8Kx8 bits SRAM

6264

A0

A1

A2

A3

A4

A5

A6

A7

A8

A9

A10

A11

A12

CS2

I/O0

I/O 1

I/O 2

I/O 3

I/O 4

I/O 5

I/O 6

I/O 7

CS1

OE

WE

6264 Block Diagram

6264 Function Table

Memory Chip

• 8K EPROM

• to be specific:– 8Kx8 bits EPROM

2764

A0

A1

A2

A3

A4

A5

A6

A7

A8

A9

A10

A11

A12

VPP

Q0

Q1

Q2

Q3

Q4

Q5

Q6

Q7

C

G

P

2764 Block Diagram

Chip enable

Output enable

Operating Modes

Programming 2764

• after each erasure for UV-EPROM):– all bits of the M2764A are in the “1" state.

• The only way to change a “0" to a ”1" is by ultraviolet light erasure.

• Programming mode when:– VPP input is at 12.5V

– E and P are at TTL low.

• The data to the data output pins.

• The levels required for the address and data inputs are TTL.

8088Minimum

Mode

A12

A0:

D7

D0:

MEMRMEMW

A13A14

8KB#2

A12

A0:

D7

D0:

RDWR

CS

8KB#1

A12

A0:

D7

D0:

RDWR

CS

8KB#128

A12

A0:

D7

D0:

RDWR

CS

A15A16A17A18A19

::

Microprocessor System Design

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