>>>The Following originally appeared in the "the kaypro column",
Microcornucopia, PO Box 223, Bend, OR 97709, by Dave Thompson.
Enjoy>>>Ben Peirce, Venice Beach>>>
>>>Speeding things up (from Micro C, June '83)>>>
The Kaypro can easily be converted from 2.5 to 5 MHz with just a
few jumpers, a faster CPU (Z80B), a new monitor ROM, and a SPDT
switch!
Replace your Z80A CPU with a 6 MHz Z80B CPU (about $13.00 from:
JDR Microdevices, 1224 A. Bascom Ave., San Jose, CA 95128,
1/800/538-5000 or 1/800/662-6279 <in Cal>). Also replace your
monitor ROM (marked with a white label as 81-149) with a new
monitor ROM capable of 5 MHz operation without overheating. You
may not have to replace the monitor ROM chip (#2716) if your
original can run at 5.0 MHz without heating up and getting silly.
Barry Cole told me that lots of "2716's" can run that fast
without problems, but mine sure couldn't! (For about $29.00 from
Micro C, PO Box 223, Bend, OR 97709, 1/503/382-8048, you can get
one that can take the heat. It also replaces the flashing cursor
with a solid one.) <an alternate way of dealing with this problem
is to use the 4 MHz clock from pin 6 of U87, instead the 5 MHz
clock from pin 5 of U86 so things don't heat up so much; the
difference between 5 and 4 MHz is insignificant>.
Remove U87 (75lS390). Cut pin 9 (or bend it out) also bend out
pin 1. Jumper pin 1 to pin 6. Jumper pin 12 to pin 15. Put the
74lS390 back in it's socket, making sure the pin 1 and pin 9
aren't making contact with anything.
Unplug U66 (74164) and bend out pins 4 and 5 so they
won't go back into the socket. Put U66 back in it's socket and
connect the trace that used to go to pin 4 to the trace that goes
to pin 3 and connect the trace that used to go to pin 5 to pin 4.
Unplug U86 (74LS293) and bend out pins 4 and 5 ( 2.5 MHz and 5
MHz clocks, respectively). Connect a lead from each of these pins
to either side of a small SPDT (single pole/double throw) switch.
Connect the center of the switch to the forward end of R26 (the
end of resistor R26 that's nearest the front of the Kaypro), so
that you will be able to select between the 2.5 MHz and 5 MHz
clock speeds. You can mount the switch quite easily in one of the
ventilation slotes on the back. The slots are just the right
width for the small toggle variety so you don't need to modify
the cabinet at all.
The early versions of disk format and copy programs don't work
with the faster clock. So you may need to slow the system down
once in a while. You will usually need to do a hardware reset
when you change speeds since the glitch usually sends the system
out to pasture!
--end--
