;******************************************************
.include "1200def.inc"
;******************************************************
;
;8 channel PWM routine. All the actiion is during the interrupt time (nothing happens
;during non-interrupt time except waiting for interrupts). There is only
;one suroutine, and its called before the interrupt, so this only uses one
;level of the stack (and an AT90S1200 doesn''t have much stack space to start with).
;
;This can be made faster by changing the interrupt timer reload value. $ED looks safe.
;It can also go faster (have a higher minimum pulse fequency) if there are fewer
;PWM channels or less resolution on the pulse width
;.
.def tempcounter = r1 ;variable used to reverse order of bits
.def pwmvalue = r2 ;variable used to reverse order of bits
.def pwmvalue0 = r3 ;duty cycle
.def pwmvalue1 = r4 ;duty cycle
.def pwmvalue2 = r5 ;duty cycle
.def pwmvalue3 = r6 ;duty cycle
.def pwmvalue4 = r7 ;duty cycle
.def pwmvalue5 = r8 ;duty cycle
.def pwmvalue6 = r9 ;duty cycle
.def pwmvalue7 = r10 ;duty cycle
.def oldticks = r11 ;variable used to decide when to make a pulse
.def ticks = r12 ;relative interrupt number mod 8
.def bout = r19 ;temporary buffer for output port b
.def temp = r20 ;scratch register for non-interrupt times
.def itemp = r21 ;scratch register for interrupt times
;having separate scratch registers saves stack space and time.
.ORG $0000
rjmp start
.ORG $0002
rjmp timerservice
rjmp start
rjmp start
rjmp start
start:
ldi temp, $01; use temp to initaize prescaler to divide by 1
out TCCR0, temp
ldi temp,$E0; use temp to initialize counter
out TCNT0,temp
ldi temp, $02; use temp to initialize TIMSK
out TIMSK,temp
ldi temp, $FF;set port B as output port
out DDRB,temp
ldi temp,$02 ;Enable timer interrupt
out TIMSK,temp
ldi temp,$00
mov ticks,temp
ldi temp,$00; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue0, pwmvalue
ldi temp,$01; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue1, pwmvalue
ldi temp,$02; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue2, pwmvalue
ldi temp,$0A; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue3, pwmvalue
ldi temp,$80; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue4,pwmvalue
ldi temp,$A0; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue5, pwmvalue
ldi temp,$E0; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue6, pwmvalue
ldi temp,$FF; test value for pwm value
mov pwmvalue,temp
rcall reversepwmvalue
mov pwmvalue7, pwmvalue
sei ; enable interrupts
loop: ;wait here for interrupt
rjmp loop
;REVERSE BIT ORDER OR PWMVALUE. Midifies pwmvalue, uses temp
reversepwmvalue: ; reverse bit order in pwmvale.
ldi temp,$08 ; 8 times through loop because there are 8 bits
mov tempcounter,temp
rotateagain:
rol pwmvalue
ror temp
dec tempcounter
brne rotateagain
mov pwmvalue,temp
ret
timerservice:
ldi itemp,$b4;set 75 clocks until next interrupt
out TCNT0,itemp
out portb,bout;transfer portb buffer to port b
andi bout,$00;preset all PWM bits to zero
mov oldticks,ticks;copy interrupt counter to temp
inc ticks ;increment interrupt timer
eor oldticks,ticks;do X-OR and AND to find bits that changed to 1 (result in temp)
and oldticks,ticks;do AND to find bits that just changes to a 1
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 0
mov itemp,oldticks
and itemp,pwmvalue0;AND to find if ones in data correspond to this interrupt count change
breq dontset0 ; if ones present, set lsb in portb buffer
ori bout,$01
dontset0:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 1
mov itemp,oldticks
and itemp,pwmvalue1;AND to find if ones in data correspond to this interrupt count change
breq dontset1 ; if ones present, set lsb in portb buffer
ori bout,$02
dontset1:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 2
mov itemp,oldticks
and itemp,pwmvalue2;AND to find if ones in data correspond to this interrupt count change
breq dontset2 ; if ones present, set lsb in portb buffer
ori bout,$04
dontset2:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 3
mov itemp,oldticks
and itemp,pwmvalue3;AND to find if ones in data correspond to this interrupt count change
breq dontset3 ; if ones present, set lsb in portb buffer
ori bout,$08
dontset3:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 3
mov itemp,oldticks
and itemp,pwmvalue4;AND to find if ones in data correspond to this interrupt count change
breq dontset4 ; if ones present, set lsb in portb buffer
ori bout,$10
dontset4:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 3
mov itemp,oldticks
and itemp,pwmvalue5;AND to find if ones in data correspond to this interrupt count change
breq dontset5 ; if ones present, set lsb in portb buffer
ori bout,$20
dontset5:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 3
mov itemp,oldticks
and itemp,pwmvalue6;AND to find if ones in data correspond to this interrupt count change
breq dontset6 ; if ones present, set lsb in portb buffer
ori bout,$40
dontset6:
; OUTPUT PWM COMB WAVEFORM TO PORTB BIT 3
mov itemp,oldticks
and itemp,pwmvalue7;AND to find if ones in data correspond to this interrupt count change
breq dontset7 ; if ones present, set lsb in portb buffer
ori bout,$80
dontset7:
reti;finished with interrupt service
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