Fabio
just checked the Texas Instruments datasheet for the standard 8224 and the max frequency is specified as 27Mhz, this should get you to 3Mhz CPU
if you cant find the faster version.
Start with a slower clock speed first to get things working then bring the speed up.
regards
David Fry
On Wednesday, April 30, 2014 7:08:07 PM UTC+1, Fabio Battaglia wrote:
Hello everyone,
I know this might not be the best place to ask for spare ICs, but the question is somewhat related to the group.
Yesterday I completed my first N8VEM Z80 cpu card, but I have another S-100 z80 board near completion: an Ithaca Audio Z80 CPU rev.2 card.
I have most of the components needed for this vintage board, and what I don't have I replaced with pin-compatible more recent chips, but I'm left with a missing component: the clock generator.
The manual specifies that the 2Mhz version used a plain 8224 coupled with a 18Mhz crystal, and an 8224-4 (actually, an AM8224-4DC) chip with a 36Mhz crystal for the 4Mhz version.
While the plain 8224 is quite easy to get (there is also a 74' clone), the 8224-4 chip required for faster clock is proving to be very elusive: I checked eBay, UTSource and tried a google search for a reseller. I only one in USA with a small stock, but they only sell to companies.
So, do anyone have some pointers on where to look for the chip? Alternatively, if someone has a spare to sell, I'd love to use it to bring my board up. If I'm unable to find one, I'll settle with a 2Mhz board, as building this board is mostly for the fun-factor.
Bye!
Fabio