4.6 PAK with Mainboard Clock Greater Than 8MHz
Page 19
PAK68/3
As a guidleine for 12MHz bus clock: R41=430 ohms, R43=330
ohms.
In addition it may be necessary to lower the bus terminations of
the mainboard. Again as a guide, 4.7k for the data lines and
3.3k for the address lines.
Sometimes it is even necessary to replace the mainboard RAM
data bus drivers. From experience we can say that at an 8MHz
board clock HCT-types are best for the two 74LS244 and for the
two 74LS373 the F-types are best. At 12MHz F-types should be
used for all drivers.
Attention! Please do not use ACT-types! While these are very
fast, they do more damage to the waveform with too much drive
power than their speed can ever make up for.
4.7 PAK and PuPla/?
We should briefly mention a very important extension to the
PAK here; the buffer board PuPla. Now available in the second
version (PuPla/2), this extension is an important tool to solve a
variety of mainboard related issues. The PuPla/2 even helps
with frequent FPU errors. The essential function of the buffer
board is to disconnect the PAK bus from the mainboard bus so
that the slow mainboard cannot disturb the PAK on local bus
cycles after a mainboard bus cycle. Additionally the PuPla/2
relieves the CPU significantly on the address and data lines. It
has an especially postive effect with a FRAK/? because the
CPU is already warm enough. More information can be found at
our website (www.wrsonline.de) or directly from us.
5. Troubleshooting
The PAK is not a real plug&play system. Unfortunately some
things have to be optimized or retrofitted by hand.