AN2475 Freescale Semiconductor / Motorola, AN2475 Datasheet - Page 11

• Manufacturer Part Number: AN2475
• Description: Generating a PWM Signal Modulated by an Analog Input Using the MC68HC908QY4 Microcontroller
• Manufacturer: Freescale Semiconductor / Motorola

SetPwmDc:
IncPwm:
WaitReg:
DecPwm:
IncPeriod:
MOTOROLA
bra
bset
lda
cmp
beq
bmi
ldx
lda
sub
cmp
bmi
incx
stx
stx
lda
cmp
bge
lda
nsa
nsa
deca
bne
bra
ldx
lda
cmp
bmi
decx
stx
stx
lda
cmp
bmi
lda
bra
lda
cmp
beq
lda
inca
clrh
sta
ldx
div
tax
stx
RegRes
PTB0,PTB
ADR
#RegVal
WaitReg
DecPwm
PWMLow
TMODL
TCH0L
PWMLim
IncPeriod
PWMLow
TCH0L
ADR
#RegHLim
IncPeriod
#$FF
WaitReg
SetPwmDc
PWMLow
PWMLow
PWMLim
DecPeriod
PWMLow
TCH0L
ADR
#RegLLim
DecPeriod
#$FF
WaitReg
TMODL
#$FF
Error
TMODL
TMODL
#$02
PWMLow
Generating a PWM Signal Modulated by an Analog Input
Freescale Semiconductor, Inc.
For More Information On This Product,
Using the MC68HC908QY4 Microcontroller
Go to: www.freescale.com
;PTB0 = 1, MCU is regulating or trying to do so
;Read ADC input value
;Compare ADC value with Target Reg. Value
;If ADC = RegVal -> wait for regulation
;If ADC < RegVal -> decrement PWM
;Verify if PWM reached its resolution limit
;Increment Period if so
;Increment PWM value
;Verify if ADC value is greater than or
;equal to Reg High Limit -> Inc Period if so
;Wait ~0.8ms or 2550 cycles to achieve accurate
;load regulation
;Verify if PWM reached its resolution limit
;Decrement Period if so
;Decrement PWM value
;Verify if ADC value is lower than
;Reg Low Limit -> Decrement Period if so
;Verify if Period is at high limit
;Go to Error Status if so
;Increment period
;Set PWM Duty Cycle to ~ 50%
Software Listing
AN2475/D
11