an introduction to assembler

7/27/2019 An Introduction to Assembler

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Introduction The PIC 18 Series Instruction Set

Byte-oriented file register operations

Bit-oriented file register operations Literal and control operations

Instruction Formats

Operation Types

MPASM Assembler

Example

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Micro-controller Programming Options:

1. Machine Code

00 0111 0001 01012. Assembly Language: needs an assembler

addwf NUM, w

3. High-Level Language: needs a compiler

for (i=0; i<10; i++) sum += a[i];

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77 instructions Three Groups:

1. Byte-oriented file register operations

2. Bit-oriented file register operations

3. Literal and control operations

Operation Types:◦ Arithmetic – Logic

◦ Data movement – Control

◦ Misc

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Format: op f, d ◦ op: operation

◦ f: number of file or register

◦ d : destination (0: working register, 1: file register)

Example:addwf PORTA, 0

Adds the contents of the working register and

register PORTA, puts the result in the workingregister.

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Format: op f, b◦ op: operation

◦ f: number of file or register

◦ b: bit number, 0 through 7

Example:bsf STATUS, 5

Sets to 1 Bit 5 of register STATUS.

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Format: op k◦ op: operation

◦ k: literal, an 8-bit if data or 11-bit if address

Examples:

addlw 5

Adds to the working register the value 5.call 9

Calls the subroutine at address 9.

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Mnemonic Operands Description CyclesStatus

Affected

ADDWF f, d Add W and f 1 C,DC,Z

COMF f, d Complement f 1 ZDECF f, d Decrement f 1 Z

INCF f, d Increment f 1 Z

SUBWF f, d Subtract W from f 1 C,DC,Z

ADDLW k Add literal and W 1 C,DC,Z

SUBLW k Subtract W from literal 1 C,DC,Z

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Affected

ANDWF f, d AND W with f 1 Z

IORWF f, d Inclusive OR W with f 1 Z

XORWF f, d Exclusive OR W with f 1 Z

ANDLW k AND literal with W 1 Z

IORLW k Inclusive OR literal with W 1 ZXORLW k Exclusive OR literal with W 1 Z

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Affected

MOVF f, d Move f 1 Z

MOVWF f Move W to f 1SWAPF f, d Swap nibbles in f 1

MOVLW k Move literal to W 1

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Affected

DECFSZ f, d Decrement f, Skip if 0 1 (2)

INCFSZ f, d Increment f, Skip if 0 1 (2)BTFSC f, b Bit Test f, Skip if Clear 1 (2)

BTFSS f, b Bit Test f, Skip if Set 1 (2)

CALL k Call subroutine 2

GOTO k Go to address 2RETFIE - Return from interrupt 2

RETLW k Return with literal in W 2

RETURN - Return from Subroutine 2

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Mnemonic Operands Description Cycles StatusAffected

CLRF f Clear f 1 Z

CLRW - Clear W 1 Z

NOP - No Operation 1RLF f, d Rotate Left f through Carry 1 C

RRF f, dRotate Right f through

Carry1 C

BCF f, b Bit Clear f 1

BSF f, b Bit Set f 1

CLRWDT - Clear Watchdog Timer 1 TO',PD'

SLEEP - Go into standby mode 1 TO',PD'

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Assembler

directiveSummary of action

list Implement a listing option

#include Include additional source file

org Set program origin

equDefine an assembly constant; this

allows us to assign a value to a label

end End program block

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Radix Example

Decimal D’255’

HexadecimalH’8d’ or 0x8d

Octal O’574’

Binary B’01011100’

ASCII ‘G’ or A’G’

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;***************************************************

;This program moves push button switch values from

;Port A to the leds on Port B

;***************************************************

;

;Configuration Word: WDT off, power-up timer on,

; code protect off, RC oscillator

;

list p=18F4550

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;

;specify SFRs

status equ 03

porta equ 05

trisa equ 05

portb equ 06

trisb equ 06

;

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;

org 00

;Initialise

start bsf status,5 ;select memory bank 1

movlw B’00011000’

movwf trisa ;set port A direction

movlw 00

movwf trisb ;all port B bits output

bcf status,5 ;select bank 0

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;

;The "main" program starts here

clrf porta ;clear all bits in ports A

loop movf porta,0 ;move port A to W register

movwf portb ;move W register to port B

goto loop

end

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an introduction to assembler

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