Question

Write the Assembly Code for PIC16F84A microcontroller to read a switch connected to Bit 2 of PORTB. You will need to first set the pin to an input, then test whether the pin is 0 ( switch closed, if so go to existing program at label SWITCH If not the program is to continue: Add comments to each line to explain what the code does.

Answer 1

FILE: helloLed.asm

; AUTH: P.Oh

; DATE: 1.0 - 04/13/02 15:09

; DESC: 1.0 - Makes B0,B2,B4,B6 LO and B1,B3,B5,B7 HI

; NOTE: Tested on PIC16F84-04/P.  

; Page numbers in code are in Easy Pic'n book

; REFs: Easy Pic'n p. 23 (Predko p. 173 is bogus?)

list p=16F84

radix hex

;-----------------------------------

; cpu equates (memory map)

myPortB equ 0x06 ; (p. 10 defines port address)

;---------------------------------

org 0x000

start movlw 0x00 ; load W with 0x00 make port B output (p. 45)

tris myPortB ; copy W tristate, port B outputs (p. 58)

movlw b'10101010' ; load W with bit pattern (p. 45)

movwf myPortB ; load myPortB with contents of W (p. 45)

circle goto circle ; done

end

;--------------------------------------

; at blast time, select:

; memory uprotected

; watchdog timer disabled

; standard crystal (4 MHz)

; power-up timer on