Embedded System Design - HCMUTbmthanh/ESD/Ch5_p2_v1.pdf · • PIC 16F877A datasheet • PIC C Help 2. Bùi Minh Thành - Bộ môn KỹThuậtĐiệnTử - ĐHBK Outline 1.PIC16

ĐẠI HỌC QUỐC GIA TP.HỒ CHÍ MINH

TRƯỜNG ĐẠI HỌC BÁCH KHOAKHOA ĐIỆN-ĐIỆN TỬ

BỘ MÔN KỸ THUẬT ĐIỆN TỬ

Bùi Minh Thành – Bộ Môn Kỹ Thuật Điện Tử - ĐHBK 11

Embedded System Design

Chapter 5: C Peripheral Interfaces

(Part 2)

Bùi Minh Thành - Bộ môn Kỹ Thuật Điện Tử - ĐHBK

References

• Martin Bates, “Programming 8-bit PIC Microcontrollers in C”, Newnes, 2008

• PIC 16F877A datasheet

• PIC C Help

2

http://www.elsevier.com/wps/find/bookdescription.cws_home/714793/description


Outline

1.PIC16 C Analog Input

2.PIC16 C Interrupts

3.PIC16 Hardware Timers

3


Outline




4


1. PIC16 C Analog Input

• Allows an external voltage to be converted to digital form, stored and processed

• This type of input occurs in data loggers, control systems, digital audio and signal processors…

• The dsPIC range is designed specifically for high-speed analog signal processing

5


Analog Setup

• The PIC 16F877 has eight analog inputs: RA0, RA1, RA2, RA3, RA5, RE0, RE1, RE2 being renamed AN0 to AN7.

6

RA0/AN02

RA1/AN13

RA2/AN2/VREF-4

RA4/T0CKI6

RA5/AN4/SS7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

OSC1/CLKIN13

OSC2/CLKOUT14

RC1/T1OSI/CCP216

RC2/CCP117

RC3/SCK/SCL18

RD0/PSP019

RD1/PSP120

RB7/PGD40

RB6/PGC39

RB538

RB437

RB3/PGM36

RB235

RB134

RB0/INT33

RD7/PSP730

RD6/PSP629

RD5/PSP528

RD4/PSP427

RD3/PSP322

RD2/PSP221

RC7/RX/DT26

RC6/TX/CK25

RC5/SDO24

RC4/SDI/SDA23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI15

MCLR/Vpp/THV1

U1

PIC16F877


A/D Block diagram

7


CCS C Analog Input Functions

8


Example

9

RA0/AN02

RA1/AN13

RA2/AN2/VREF-4

RA4/T0CKI6

RA5/AN4/SS7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

OSC1/CLKIN13

OSC2/CLKOUT14

RC1/T1OSI/CCP216

RC2/CCP117

RC3/SCK/SCL18

RD0/PSP019

RD1/PSP120

RB7/PGD40

RB6/PGC39

RB538

RB437

RB3/PGM36

RB235

RB134

RB0/INT33

RD7/PSP730

RD6/PSP629

RD5/PSP528

RD4/PSP427

RD3/PSP322

RD2/PSP221

RC7/RX/DT26

RC6/TX/CK25

RC5/SDO24

RC4/SDI/SDA23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI15

MCLR/Vpp/THV1

U1

PIC16F877

VSS

RXD

VDD

LCD1

MILFORD-2X16-BKP

RV1

1k


Example

10


Voltage measurement

11

RA0/AN02

RA1/AN13

RA2/AN2/VREF-4

RA4/T0CKI6

RA5/AN4/SS7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

OSC1/CLKIN13

OSC2/CLKOUT14

RC1/T1OSI/CCP216

RC2/CCP117

RC3/SCK/SCL18

RD0/PSP019

RD1/PSP120

RB7/PGD40

RB6/PGC39

RB538

RB437

RB3/PGM36

RB235

RB134

RB0/INT33

RD7/PSP730

RD6/PSP629

RD5/PSP528

RD4/PSP427

RD3/PSP322

RD2/PSP221

RC7/RX/DT26

RC6/TX/CK25

RC5/SDO24

RC4/SDI/SDA23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI15

MCLR/Vpp/THV1

U1

PIC16F877

VSS

RXD

VDD

LCD1

MILFORD-2X16-BKP

D1

BZX79C2V7

R1680R

RV2

1k

R24k7

RV1

1k

RV3

1k

RV4

1k

RV5

1k

RV6

1k

RV7

1k

RV8

1k

R3

120R

U1(RA3/AN3/VREF+)V=2.55838

RV5(1)V=2.71739


Voltage measurement

12


Outline




13


2. PIC16 C Interrupts

• Interrupts allow an external event to initiate a control sequence that takes priority over the current MCU activity.

• The interrupt service routine (ISR) carries out some operation associated with the port or internal device that requested the interrupt.

• Interrupts are frequently used with hardware timers, which provide delays, timed intervals and measurement.

• PIC16F877 has 14 interrupt sources

14


C Interrupts

• CCS C Interrupt Functions

15


C Interrupts – Interrupt sourcesPIC16 F877 Primary Interrupt

16

PIC16 F877 Peripheral Interrupts


Interrupt Sources

17


Interrupt example

18

RA0/AN02

RA1/AN13

RA2/AN2/VREF-4

RA4/T0CKI6

RA5/AN4/SS7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

OSC1/CLKIN13

OSC2/CLKOUT14

RC1/T1OSI/CCP216

RC2/CCP117

RC3/SCK/SCL18

RD0/PSP019

RD1/PSP120

RB7/PGD40

RB6/PGC39

RB538

RB437

RB3/PGM36

RB235

RB134

RB0/INT33

RD7/PSP730

RD6/PSP629

RD5/PSP528

RD4/PSP427

RD3/PSP322

RD2/PSP221

RC7/RX/DT26

RC6/TX/CK25

RC5/SDO24

RC4/SDI/SDA23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI15

MCLR/Vpp/THV1

U1

PIC16F877

R110k

X1

4MHz

1

2

3

4

5

6

7

8

20

19

18

17

16

15

14

13

9

10

12

11

U2

2

3

4

5

6

7

8

9

1

RP1

220R

C1

15pF

C2

15pF


Interrupt example

19


Interrupt statements

• #int_xxx– Tells the compiler that the code immediately following is the

service routine for this particular interrupt

– The interrupt name is preceded by #(hash) to mark the start of the ISR definition and to differentiate it from a standard function block.

– An interrupt name is defined for each interrupt source.

• enable_interrupts(int_ext);– Enables the named interrupt by loading the necessary codes

into the interrupt control registers

20


Interrupt statements

• enable_interrupts(level);– Enables the interrupt at the given level.

– Examples: enable_interrupts(GLOBAL);

enable_interrupts(INT_TIMER0);

enable_interrupts(INT_TIMER1);

• Disable_interrupts(level)– Disable interrupt at the given level

• ext_int_edge(H_TO_L);– Enables the edge on which the edge interrupt should trigger.

This can be either rising or falling edge.

21


Timer interrupt process

22


Outline




23


3. PIC16 Hardware Timers

• The PIC 16F877 has three hardware timers built in: Timer0 (8-bit) (originally called RTCC, the real-time counter clock), Timer1 (16-bit), and Timer2 (8-bit).

• The principal mode of operation of these registers are as counters for external events or timers using the internal clock.

• Additional registers are used to provide Capture, Compare, and Pulse Width Modulation (PWM) modes

24


Counter/Timer Operation

• A counter/timer register consists of a set of bistable stages (flip-flops) connected in cascade (8, 16, or 32 bits).

• An 8-bit counter counts up from 0x00 to 0xFF 25

Flag is set to 1 when overflow (7 to 0)


Counter/Timer Operation

• Timer0 is an 8-bit register that can count pulses at RA4; for this purpose, the input is called T0CKI (Timer0 clock input).

• Timer1 is a 16-bit register that can count up to 0xFFFF (65,535) connected to RC0 (T1CKI) .

• The count can be recorded at any chosen point in time; alternatively, an interrupt can be generated on overflow to notify the processor that the maximum count has been exceeded.

• If the register is preloaded with a suitable value, the interrupt occurs after a known count.

• Timer0 has a prescaler that divides by up to 128;

• Timer1 has one that divides by 2, 4, or 8;

• Timer2 has a prescaler and postscaler that divide by up to 16.

26


Timer Functions

27


Exercise

28

A7

A7

L0

L7

A6

A4

A3

A1

A2

A0

A0

A1

A2

A3

A4

A5

A6

L1

L2

L3

L4

L5

L6

L7

L0

L1

L2

L3

L4

L5

L6

C7

C3

C0

C1

C2

C4

C5

C6

C7

C6 C

5

C4 C

3 C1

A5

C0

C2

RA0/AN02

RA1/AN13

RA2/AN2/VREF-/CVREF4

RA4/T0CKI/C1OUT6

RA5/AN4/SS/C2OUT7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

OSC1/CLKIN13

OSC2/CLKOUT14

RC1/T1OSI/CCP216

RC2/CCP117

RC3/SCK/SCL18

RD0/PSP019

RD1/PSP120

RB7/PGD40

RB6/PGC39

RB538

RB437

RB3/PGM36

RB235

RB134

RB0/INT33

RD7/PSP730

RD6/PSP629

RD5/PSP528

RD4/PSP427

RD3/PSP322

RD2/PSP221

RC7/RX/DT26

RC6/TX/CK25

RC5/SDO24

RC4/SDI/SDA23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI15

MCLR/Vpp/THV1

U1

PIC16F877A

R110k

2

3

4

5

6

7

8

9

1

RP1

RESPACK-8

D1LED-BIRY

D2LED-BIRY

D3LED-BIRY

D4LED-BIRY

D5LED-BIRY

D6LED-BIRY

D7LED-BIRY

D8

LED-BIRY

A7

QA13

B1

QB12

C2

QC11

D6

QD10

BI/RBO4

QE9

RBI5

QF15

LT3

QG14

U2

74LS47

100%

RV1

1k

+88.8

Volts

+88.8

Volts

Bùi Minh Thành - Bộ môn Kỹ Thuật Điện Tử - ĐHBK 29

The program that carries out

the function of a counting

circuit counts from 00 to 19

and displays on two 7-seg

leds connected to port C


C source code with Assembly block

30

If the MCU clock

is 20MHz

the output

frequency is

1.25MHz.


PWM mode

• In Pulse Width Modulation mode, a CCP module can be used to generate a timed output signal.

• This provides an output pulse waveform with an adjustable high (mark) period.

31


PWM mode - Example

32

Produce an output at CCP1 of 250Hz (4ms) and a mark-space ratio of 50%

with a 4-MHz MCU clock. Explain?


Compare Mode

• Generate a timed output in conjunction with Timer1.

• The 16-bit CCPR register is preloaded with a set value, which is continuously compared with the Timer1 count. When the count matches the CCPR value, the output pin toggles and a CCP interrupt is generated. If this operation is repeated, an interrupt and output change with a known period can be obtained.

33


Capture mode• The CCP pin is set to input and monitored for a change of state.

• When a rising or falling edge (selectable) is detected, the timer register is cleared to 0 and starts counting at the internal clock rate.

• When the next active edge is detected at the input, the timer register value is copied to the CCP register. The count therefore corresponds to the period of the input signal. With a 1MHz instruction clock, the count is in microseconds

34


Exercise – Timer Interrupt

35

1) Calculate the

frequency of the pulse

on PIN B0 created by

the program on the

right figure, given that

FOSC = 4MHz

2) Write the program that

create a 2Hz pulse on

PIN_B1, given that

FOSC = 4MHz and

dutycycle = 20%

Documents

Embedded System Design - HCMUTbmthanh/ESD/Ch5_p2_v1.pdf · • PIC 16F877A datasheet • PIC C Help 2. Bùi Minh Thành - Bộ môn KỹThuậtĐiệnTử - ĐHBK Outline 1.PIC16