Post by thread:Can't change prescaler for TIMER2 on 16C74

I am using the PWM module on the '74, and have been succesful in getting an output from the CCP1 module. I can vary the duty cycle with no problem. The problem is that the PWM frequency is too low. I am using a 19.6608 Mhx crystal, and the PWM frequency results in 1.2 kHz. From all indications, the prescaler is set to 1:16, and I need a ratio of 1:1. I tried changing the prescaler by flipping the bits in T2CON, but nothing happens. Here is my init code : MOVLW H'04' ;Timer 2 on, prescaler = 1 MOVWF T2CON MOVLW B'00001100' ;PWM ON MOVWF CCP1CON MOVLW H'FF' ;PR2 = OXFF MOVWF H'80'^PR2 The databook says that T2CON controls the prescaler, but it does not work. I have tried with three '74 so far. Have I done something wrong or is there a bug? My machine will be done for service starting on 12/27, please reply soon. Many, many thanks! +---------------------------------------------------------------------------+ | Edward Cheung, Ph.D. | The opinions expressed herein | | NASA Goddard Space Flight Center | do not necessarily reflect | | Mail Code J&T/442 | those of my employers' | | Greenbelt, MD 20771 | | | 301-286-1269(office) 286-1717(fax) | My next book: | | Internet: spam_OUTedward.cheungTakeThisOuTgsfc.nasa.gov | Statistics, Demos and Other Lies | +---------------------------------------------------------------------------+

In a previous message I wrote: >My machine will be done for service starting on 12/27, please reply soon. I meant to say: My machine will be down for service starting on 12/27 ^^^^ Thanks +---------------------------------------------------------------------------+ | Edward Cheung, Ph.D. | The opinions expressed herein | | NASA Goddard Space Flight Center | do not necessarily reflect | | Mail Code J&T/442 | those of my employers' | | Greenbelt, MD 20771 | | | 301-286-1269(office) 286-1717(fax) | My next book: | | Internet: .....edward.cheungKILLspam@spam@gsfc.nasa.gov | Statistics, Demos and Other Lies | +---------------------------------------------------------------------------+

In a message dated 95-12-26 09:03:16 EST, you write: > Here is >my init code : > > MOVLW H'04' ;Timer 2 on, prescaler = 1 > MOVWF T2CON > MOVLW B'00001100' ;PWM ON > MOVWF CCP1CON > MOVLW H'FF' ;PR2 = OXFF > MOVWF H'80'^PR2 Presumably in actuality you set RP0 before you store in RP2, which is in bank 1? ...Shel Michaels

From me: > MOVLW H'04' ;Timer 2 on, prescaler = 1 > MOVWF T2CON > MOVLW H'FF' ;PR2 = OXFF > MOVWF H'80'^PR2 From the wise one: Shel Michaels <SbmichaelsKILLspamAOL.COM> >Presumably in actuality you set RP0 before you store in RP2, which is in bank >1? ARRGGHHH!! You are right! By not setting the page bit, the above operation stores 0xFF into T2CON, erasing the 0x04 I put in earlier. I suppressed the warning by using the ^0x80, but forgot to set the page bit. Many thanks! +---------------------------------------------------------------------------+ | Edward Cheung, Ph.D. | The opinions expressed herein | | NASA Goddard Space Flight Center | do not necessarily reflect | | Mail Code J&T/442 | those of my employers' | | Greenbelt, MD 20771 | | | 301-286-1269(office) 286-1717(fax) | My next book: | | Internet: .....edward.cheungKILLspam.....gsfc.nasa.gov | Statistics, Demos and Other Lies | +---------------------------------------------------------------------------+