Re: 14MHz Osc Chip Question

["Bryan Parkoff" <BParkoff@satx.rr.com>]

> What makes you think that?  If you replace the 14.318 MHz crystal in an
> Apple ][, ][+, //e, or //c with a higher frequency, all the machine
> timing including video will change, because it's all derived from that
> 14.318 MHz crystal.  Almost everything in the computer, including some
> peripherals like the floppy controller, are carefully designed based on
> the precise timing.  Basically most everything won't work at a different
> frequency.
    If TransWarp or ZipCard are used, do they disable 14.318 MHz crystal
chip while another higher crystal chip is executing for 6502 CPU?  What is
the difference that Apple IIgs operate?

> The 14.31818 MHz clock is divided by 14 to produce the CPU clock.  (One
> out of every 65 CPU clocks is stretched a bit, but we can ignore that
> for now.)  The resulting signal has a period of 978 ns.  It spends about
> 489 ns high and 489 ns low (actually slightly less since the transistion
> takes a few ns).  The 6502 only uses the half of the cycle when the clock
> is high to perform a memory access.  The Apple circuitry uses the other
half
> of the cycle, while the clock is low, to perform a memory access for video
> (and memory refresh).
    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".
    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?

Yours Truly,

Bryan Parkoff
BParkoff@satx.rr.com