;

; Example Program for Lab 8

; Coded for use on EVB, changes required for use on THRSim11

; Program Inputs: None

; Program Outputs: 1. Prints ASCII 1 or 0 to screen

; 2. Toggles Pin7 of PortA between 1 and 0

; every 1/2 second

;

PutC = bfd3

org c200

Main: lds #dfff

ldy #c000 ; Make Y point at c000

clr 0,y ; Clear c000 for use as counter

ldaa #80 ; initialize accum A with a 1 in bit 7

ldx #1000 ; Make X point at top of special registers

staa 26,x ; Make DDRA 1 (PortA = Output port)

staa 0c,x ; Make FOC control only PA7 (bit 7 of PortA)

cli

Loop: brset 25,x,80,TOFC ; poll the TOF overflow flag

bclr 23,x,7f ; clear OC1 flag if it occurs (OC1 not used)

bra Loop

TOFC: bclr 25,x,7f ; clear TOF flag

inc 0,y ; count number of TOF interrupts

brset 0,y,10,TOG ; if 16 TOFs have occurred, toggle output

bra Loop

TOG: clr 0,y ; after 16 TOF periods, reset counter

staa 0b,x ; Force an output change of PA7 pin (put

; a 1 in bit 7 of 100B, the FOC register)

ldab 100d ; load current ouput value of PA7 (0 or 1)

eorb #80 ; toggle the output value of PA7 (1 or 0)

stab 100d ; send toggled value to data register for PortA

lsrb

adab #30 ; make new value of PA7 an ASCII char

pshb ; and put it out to screen

jsr PutC

bra Loop