Alex Freed wrote:
Steven Hirsch wrote:I'm wondering how Alex was lucky enough to get an item that DigiKey shows as non-stock. And, yes, I'd also like to know if it works!Just luck. Because I didn't really care all that much :)
Seriously! You ordered a non-stock part and they shipped it?? Cool.
That would be a definite "no". By running 80nsec. DRAM (VERY expensive at the time and hard to find in a 7-bit refresh flavor),If you use 256K chips and ground the unused address pin, 70 ns parts are easy to find. However that is not the total access time. For marketing reasons the DRAM was rated in *different* ns. If you only use 64K out of 256, 7 bit refresh makes no difference. So the 256K 70 ns DRAMs are likely good up to 11-12 MHz on a good day.
Heh. At the time, 256K chips were a costly solution ($8-10 ea, IIRC, and that when a dollar was actually worth something). I'll have to try that now that I have boxes full of them :-).
replacing a few 74LS parts with HCT and trying a handful of Z80H (8Mhz. rated) chips I was able to get one of my Applicard running reliably at 10Mhz.Actually HCT is not much faster than LS. 74F is the answer these days.
You are keeping me honest. I dragged the card out and they are 74F indeed. Looks like a couple of 74F158s over next to the DRAM, a 74F74 and a 74F04 to the right of the CPU. There's also a pair of wires on the back that I have to dig out my notes to recall the purpose of..
The CPU is a Toshiba TMPZ84C00AP-8 clocked from a 20Mhz. crystal.
Alex's card uses a far simpler design with modern parts and static RAM. It's not out of the question that it could run at those speeds, but it's purely in the realm of experimentation.Actually it was *designed* to run at 20 MHz. I just didn't test it above 10 because I only got a 20 MHz z80 last week.
Great to hear.