9S08QG8 PWM in assembly

wolfgangs — Wed, 17 Jul 2013 20:14:16 GMT

Hello everyone, I am trying to program a continuous 100Hz 50% duty cycle signal on pin 16 (TPMCH0) using the 9s08qg8 in assembly. I am using the internal oscillator (FBI mode) f=16kHz. I observe some strange behavior. As soon as power is supplied to the MCU, pin 16 illuminates for about 3.5 seconds at what appears to be full duty. Even after changing various variables, this behavior continues. Can anyone help me please? Thanks.

; Include derivative-specific definitions

INCLUDE 'derivative.inc'

; export symbols to be refer. in the linker .prm file

XDEF _Startup, main

XREF __SEG_END_SSTACK

; symbol defined by the linker for the end of the stack

; variable/data section

MY_ZEROPAGE: SECTION SHORT

; no variables defined

; Code section

MyCode: SECTION

_Startup:

main: LDHX #__SEG_END_SSTACK ; init stack pointer

TXS

CLI ; enable interrupts

LDA #%01110011

STA SOPT1

MOV #%01000100,ICSC1

MOV #%00000000,ICSC2

MOV #%00001000,MTIMCLK ;timer not necessarily used.

MOV #62,MTIMMOD

MOV #%00000000,MTIMSC

MOV #156,TPMMODL ;Bus clock / TPMMODL = 15625/156=100Hz

MOV #156,TPMC0VL ;100% duty, but tried 0-100%

MOV #$28,TPMC0SC ;no interupt, edge aligned, high-true pulse

MOV #$08,TPMSC ;Edge aligned, no interupt, using bus clock, prescale=1

LOOP BRA LOOP ;run forever

SWI

;*****************************************************

; ROUTINES

;*****************************************************

;timer not necessarily used.

TIMER BRCLR 7,MTIMSC,TIMER ;WAIT FOR TOF

BCLR 7,MTIMSC ;CLEAR TOF

RTS

Re: 9S08QG8 PWM in assembly

bigmac — Thu, 18 Jul 2013 04:25:56 GMT

Hello,

There would be a problem with your code because you are writing to the low byte only of the 16-bit registers TPMMOD and TPMC0V. Both bytes require to be written for the new values to take effect. The following code snippet should achieve 50 percent PWM duty -

LDHX #155 ; Bus clock/(TPMMOD+1) = 15625 / 156 = 100Hz

STHX TPMMOD

LDHX #78 ; 50% duty

STHX TPMC0V

However, I might also expect that your bus frequency will actually be considerably higher than 15.625 kHz. I suggest that you check your ISC settings.

Regards,

Mac

Re: 9S08QG8 PWM in assembly

wolfgangs — Thu, 18 Jul 2013 20:49:43 GMT

Thanks a lot bigmac! That is exactly what I needed!

topic 9S08QG8 PWM in assembly in 8-bit Microcontrollers

9S08QG8 PWM in assembly

Re: 9S08QG8 PWM in assembly

Re: 9S08QG8 PWM in assembly