Re: 14MHz Osc Chip Question

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

"Bryan Parkoff" <BParkoff@satx.rr.com> writes:
>     My question is: If 14MHz osc chip is replaced to 25MHz osc chip, will
> 14MHz, 7MHz, 3.5MHz AND 2MHz be REMAINED THE SAME for RAM, Video Scanner,
> Video Monitor, and ETC, BUT 10MHz will be REPLACED from 1MHz for 6502 CPU to
> increase the speed?  Correct?

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.

>     (For 1MHz only) I understand that approx 17000 cycles can be executed
> every one second.  I suspect that it is approx 10 to 16 opcode instructions
> can be executed each one second WHILE approx 16500 cycles are TAKEN for RAM
> and Video Generator.  I am confused that only million opcode instructions
> can be executed each one second that is opposite to 12-16 opcode
> instructions.  Can you please explain more.  If it is the case that 1/65
> cycle can be done with opcode instruction each one second while 64/65 cycles
> can be done with RAM and Video Generator.

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).

>     I am happy that I won on eBay to purchase the Understanding the Apple II
> manual and Understanding the Apple //e manual.  They do provide the
> information about timing scheme.  I am not sure that I understand what the
> manual meant.

Those manuals provide the best explanation anywhere.  I suggest studying
them carefully and asking any specific questions here.