Re: 14MHz Osc Chip Question

[Eric Smith <eric-no-spam-for-me@brouhaha.com>]

"Bryan Parkoff" <BParkoff@satx.rr.com> writes:
>     If TransWarp or ZipCard are used, do they disable 14.318 MHz crystal
> chip while another higher crystal chip is executing for 6502 CPU?

No.  They run a separate CPU at a higher speed on the card.  They don't
interfere with the timing of the main logic board, as that would break
the video.

> What is
> the difference that Apple IIgs operate?

The IIgs has much more complex circuitry (buried in the ASICs) that allow
the CPU and memory to be run at a higher frequency than the video.  The
earlier Apple II models do not have this capability.

>     If I understand correctly, only ONE cycle can be executed at once time
> each second on 6502 CPU.  Does 65 cycles execute for one minute?  I am
> confused the words, "CPU Clock and Cycle".

The 6502 can perform one memory access for every clock cycle, so it can
perform just a bit over one million memory cycles per second in the
Apple II.  (More on the IIgs due to the fancier circuitry).

That's approximately one CPU cycle per microsecond, not one per second.
                                       ^^^^^

>     I do understand that 0.5 cycle can be executed for 6502 CPU BEFORE (NOT
> WHILE) another 0.5 cycle can be executed for RAM.  Both 0.5 cycles are equal
> to one cycle each second.  It is the way that 6502 CPU is enabled to execute
> 0.5 cycle before it is disabled.  Then RAM is enabled to execute 0.5 cycle
> before it is disabled.  It does repeat both 6502 CPU and RAM over and over
> that it becomes one cycle per second.  Does it make sense?

I think you've got the right idea, other than it being two RAM cycles per
microsecond, one for video and one for the CPU.