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EECE416: Microcomputer

Fundamentals and Design

PIC Instruction Set and SomeTips for Programming

Dr. Charles J. Kim

Howard University


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F877 Instruction Set

14-Bit Word

Byte-Oriented Instruction

F: File Register (or RAM)

D: Destination

D=0: Destination W

D=1: Destination

File Register

Bit-Oriented Instruction

B: Bit Field

F: Register File where the Bit is located Literal and Control Operation

K: 8-bit constant


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General Form of Instruction


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Instruction List


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Destination of the result & Machine Code

D=0: Destination WD=1: Destination File Register (Default)

addw f PORTD ;

Add content of PORTD to content of the W and

store the result back into PORTD

addwf PORTD, 0 ;

Add content of PORTD to content of the W andstore the result into W


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Register Addressing Modes

Immediate Addressing(ex) MOVLW 0x0F

Direct AddressingUses 7 bits of 14 bit instruction to identify a register file address

8th

and 9th

bit comes from RP0 and RP1 bits of STATUS register. Initial condition for RP0 and RP1: RP1=RP0=0

(ex) SSPCON EQU 0x14

STATUS EQU 0x03

SSPSTAT EQU 0x94BCF STATUS, 0x05

BCF SSPCON, 0x01

BSF STATUS, 0x05

BCF SSPSTAT, 0x02


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Direct Addressing - Recap


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Indirect Addressing

INDF registerAny instruction using the INDF actually accesses the register

pointed to by the File Select Register (FSR).

A 9-bit EA is obtained by concatenating the 8-bit FSRregister and the IRP bit(STATUS)

Example: Erase the RAM section of 0x20-0x2FMovlw 0x20; pointer

Movwf FSR

Next clrf INDF

incf FSR

btfss FSR, 4goto next


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Direct vs. Indirect Addressing


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Instruction Setsdescription convention


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addlw


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addwf


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andlw


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andwf


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Bcf & bsf


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btfsc


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Btfss


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Call


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CLRF & CLRW


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COMF & DECF


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DECFSZ


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GOTO & INCF


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INCFSZ


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IORLW & IORWF


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MOVLW & MOVF


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MOVWF & NOP


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RETFIE & RETLW


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RETURN


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RLF & RRF


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SUBLW & SUBWF


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SWAPF & XORLW


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XORWF


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F877 Instruction Programming Tips

Tips on Instruction Skills and Tricks

Frequently Met Situations

(a) Turn on/off an LEDAn LED is connected to a pin at one, say,

PORTB, and to a ground at the other.

Use a bit-oriented file register operation:bsf

PORTB, 0x00

;to turn on and

BSF PORTB, 0 ;same effect

bcf PORTB, 0x00 ;to turn off.BCF PORTB, 0 ;same OFF


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(b)Variable DeclarationIn C:

byte temp

intx

In PIC:

Variables must occupy physical RAM space

CBLOCK ENDC pairExample:

Tips Variable Declaration


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(c) I/O designation to the I/O PortI/O Ports: PORTA, PORTB, PORTC, PORTD, PORTE

Bi-directional

Input or Output

I/O selection file register

TRISA for PORTA; TRISB for PORTB; TRISC for PORTC

TRISD for PORTD; TRISE for PORTE

Each pin can be selected as

1: Input

0: Output

Tips I/O designation


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(e) Reading sensor (digital) input anddecision-making based on the input

PIR motion detector & buzzer examplePIR output1: No motion detected

0: Motion detected

Buzzer

1: Buzzer On0: Buzzer Off

Use BTFSS or BTFSC

Tips Reading Sensor Input


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Sample Code

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