mcmahan@netcom.UUCP (Dave Mc Mahan) (04/09/90)
I have written a short test program that measures the frequency of the Phi-2 clock signal on the CIA-B chip. With repeated measurements over varying periods of time, I keep finding the clock frequency is about 713 KHz. Is this correct? I would have guessed that it is either the system clock (7.14 MHz) or the colorburst frequency. Are my math calculations wrong? If it IS 713 KHz, where is this generated from? -dave
rsbx@cbmvax.commodore.com (Raymond S. Brand) (04/09/90)
In article <10713@netcom.UUCP>, mcmahan@netcom.UUCP (Dave Mc Mahan) writes: > I have written a short test program that measures the frequency of the Phi-2 > clock signal on the CIA-B chip. With repeated measurements over varying > periods of time, I keep finding the clock frequency is about 713 KHz. Is this > correct? I would have guessed that it is either the system clock (7.14 MHz) > or the colorburst frequency. Are my math calculations wrong? If it IS > 713 KHz, where is this generated from? > > -dave On an NTSC machine the Phi-2 clock (E-Clock) will be at 715909hz and on a PAL machine it will be 709379hz. On 68000 based motherboards this signal comes from the E pin of the 68000, which is the processor clock divided by 10. BTW, the CIAs may be clocked at different rates on future machines. rsbx ------------------------------------------------------------------------ Raymond S. Brand rsbx@cbmvax.commodore.com Commodore-Amiga Engineering ...!uunet!cbmvax!rsbx 1200 Wilson Drive (215)-431-9100 West Chester PA 19380 "We're working on it" ------------------------------------------------------------------------
LEEK@QUCDN.QueensU.CA (04/10/90)
In article <10713@netcom.UUCP>, mcmahan@netcom.UUCP (Dave Mc Mahan) says: > >I have written a short test program that measures the frequency of the Phi-2 >clock signal on the CIA-B chip. With repeated measurements over varying >periods of time, I keep finding the clock frequency is about 713 KHz. Is this >correct? I would have guessed that it is either the system clock (7.14 MHz) >or the colorburst frequency. Are my math calculations wrong? If it IS >713 KHz, where is this generated from? > > -dave The Phi-2 (or 02) clock is generated by the E clock circuit on board the 68000. It is 1/10 of the frequency at the clock input pin of the 68000. It allows the 68000 to use the older 6800 series perpherial chip. In this case Phi-2 = 7.16 MHz/10 = 716 KHz. So your calculation is very good !!! K. C. Lee No disclaimers because no ideas were expressed... :)