PLEASE HELP! Square wave on 68HC908

[chrismac99]

Similar thread, different controller.

https://www.electro-tech-online.com/threads/pwm-assembly-code-for-68hc11.8551/



Still need help. Thanks.

 

[kchriste]

If 68HC11 code will help here is some code I wrote over 10 years ago. Don't ask me to explain it because my 68HC11 days are long forgotten. It was also written for my own homemade assembler so the syntax may seem a little odd. But it may help you anyway.

;      THIS PROGRAM WILL CONVERT THE DATA IN AN EXTERNAL RAM/ROM LOCATED
;      AT 8000-F7FF TO SOUND VIA A PWM SIGNAL AT BIT 6 ON PORT A

ldx 1000
LDS 00FF
LDAA 25
STAA/X 3C             ; TURN ON EXPANSION BUS
LDD C040
STAA/X 20             ; ENABLE PIN SETTING FOR O.C. #2
STAB/X 0C             ; ENABLE PIN CLEARING FOR O.C. #1 ON PORT A BIT 6
:START
LDY 8000              ; LOAD Y WITH START OF 32K RAM
:SOUND
LDD/X 18              ; GET OUTPUT COMPARE COUNT #2
ADDD 0140             ; ADD 320 TO O.C. COUNTER
STD/X 18              ; RESET COUNT #2
CLRA
LDAB/Y 0              ; GET SOUND BYTE
ADDD/X 18             ; GET END OF PWM PULSE
SUBD 0100             ; SUBTRACT 256 BYTES 
STD/X 16              ; PUT SOUND INTO O.C. #1
:WAIT
BRCLR/X 2340 :WAIT
LDAA 40
STAA/X 23
INY
CPY F800              ; DON'T ALLOW IT TO READ INTO EEPROM
BNE :SOUND
BRA :START