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.
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