Brian A. Davis wrote:
In article <3D950B7F.3090404@noneofyourbusiness.com>, Exegete <millers@noneofyourbusiness.com> wrote:Most computers have a number of other things that they do that also run on the same clock. Changing the clock means that those other things no longer work, like reading, writing, or formatting a disk for instance.Sorry, Roy. I was not specific enough. I have a PCPI Appli-card with a 6 MHz Z80B. On board the Appli-card is a 12 MHz oscillator. This is what I was thinking of changing. I did not mean the oscillator on the Apple IIe motherboard.The PCPI Appli-card has its own 64k RAM bank, so the only interactions between the card and the Apple IIe motheboard are I/O calls (I think).
You can soup up an Applicard without too much difficulty. I used to do this mod for friends about 15 years back <g>.
1) Replace the CPU with a Z80H (8-Mhz. clock speed). I have no idea where you might find one nowadays.
2) Replace the on-board DRAM with 80nsec. 7-bit refresh chips. This last parm is the toughest to accomodate. Spec sheets were often vague about it, and many of the faster DIP DRAM chips require 8-bit refresh and will not work properly.
3) Install a 16Mhz. crystal.4) There's a minor circuit modification which adds a previously-unused gate on one of the chips to the clock logic. This was almost always required to get them to work reliably. I had the docs on this at one point, but Lord knows where they are now.
I still have a couple of modified boards somewhere. If I trip over one of them, I'll try to remember to post the missing info about circuit changes.
Steve