68ec020 clock

[JLPedro]

The cpu clock on board shows 28,xxmhz but the amiga 1200 cpu works at a 14.xx frequency, what does it means? If i put som fast ram does the cpu works at the full speed of 28.xx mhz? i know that the a1200 cpu it's restricted by the other chips acessing the chip ram at the same time and that with fast ram the cpu it's free to operate at its full speed but from 14,xx mhz to 28.xx mhz it's a big diference.

[Harrison]

Where are you getting the CPU speed reading from? The CPU in the A1200 will always run at the 14MHz speed. The reading you are getting might be being obtained from something else in the system such as an FPU if you have one fitted to a ram expansion, or the clock speed of one of the custom chips.

[JLPedro]

I'm reading from the cristal next to the cpu, it reads 28,37516Mhz, motherboard revision 1b Pal.

Near the Kickstart chips.

[Harrison]

Oh, OK. That isn't anything to do with the CPU. That crystal oscilator you have found is used to control the speed of the Amiga's video subsystem.

[JLPedro]

Ops... amators... Thanks for the ilucidation!

[Harrison]

No Problem. Such things easily confuse.

[Zetr0]

Oscilators... hang on just spamed a post about this?

LOL

as Harrison states the 28.8 is infact the governing Clock of the A1200, most of the chips internally devide this state so in effect they are running at 14.4, although not all the chips. the 020 on the other hand has to consult to these chips and as such is bound by the governing clock of 28.8/2 (14.4) unless you run it in NTSC which has the custom chips running slightly faster.

When you add fast Ram the 020 when doing its own work doens't have to wait for access to chip ram and as such can run at the FULL governing clock speed of the card (if it has a clock) or its internal factor of the governing clock in this case its around twice as fast.

however it will slow down with the more Chip access it does,

[Harrison]

Hence that proves that it is correct that just adding a simple fast ram expansion card to the A1200 will roughly double it's CPU speed. Although not the whole system's speed as the custom chips and chip ram are still running at their same speed.