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PWM GENERATION WITH ST62 AUTO-RELOAD TIMER

Program example:

– SC0 is not programmed, so it keeps its reset value 00h (all flags cleared)

– The PWM signal starts as soon as the last instruction (ldi MC) is executed

Program example

****************** A-R Timer Register Set ********************************

RC

.def 0D9h,0FFh,0FFh

;reload/capture register

CP

.def 0DAh,0FFh,0FFh

;compare register

MC

.def 0D5h,0FFh,0FFh

;mode control register

SC0

.def 0D6h,0FFh,0FFh

;status/control register 0

SC1

.def 0D7h,0FFh,0FFh

;status/control register 1

LR

. def 0DBh,0FFh,0FFh

;load register

;============================================================

ldi CP, 186

;compare register = 186d

ldi RC, 145

;reload register = 145d

ldi SC1,001h

;clock source= CPU clock divided by 3

;prescaler ratio = 1

ldi MC, 11100000b

;auto-reload mode,interrupts disabled

;PWMOUT enabled, start timer

Example 2:

Target: generate a PWM signal of frequency 31.25 kHz with a duty cycle proportional to an

responds to 100% duty cycle. The CPU clock is 8 MHz:

Referring to example 1, we find that the prescaler ratio must be 1, the value in RC must be 0

and the value in CP is taken directly from the A/D output (varying from 0 to 255d depending

upon the analog input):

RC = 0

CP = 0...255d

prescaler ratio = 1

Duty cycle = CP / 256d

Resolution = 1/256d = 0.39 %

We need to implement a software loop which repetitively converts the analog input to a digital

value and copies this digital value into CP: