29 Sep
2011
29 Sep
'11
2:29 p.m.
On 29 Sep 2011 at 21:31, Tony Duell wrote:
Mine is currently populated for 8 input, 12 output, but has positions
for an extra 151 and one more 393. That expands it to 16 outputs,
and 20 inputs (from the DUT's perspective) (the low order 4 bits of
the first 393 drives the select on the 151s).
I've got headers on all of the outputs and inputs as well as on the
DUT socket, so it's just a matter of jumpering things how you'd like.
With a wirewrap gun, it's literally just a couple of minutes to
change the configuration.
But a uC has a huge advantage when creating a general solution, as
you don't need any sort of pin drivers--just change the programming
for the uC pins and you're all set.
I was lazy with mine--I knew that counters would work and required no
device programming, leaving the smarts on the PC side.
--Chuck
A worthwhile
project might be a cheap "universal PROM/PAL" reader.
I built one years ago, initially for the CoCo, I later used in on an
MS-DOS machine.
It consists of 16 output lines (notionally address, but could be used
for enables/clocks where nexcessoar), 8 input lines (used to read in
the data), and +/-5V, +/-12V power lines. The CoCO version used TTL
latches and buffers, the PC version used an 8255 PCB from Maplin. A
manual toggle swithc tri-states all ouytput lines and turns off the
PSU rails so you can safely insert/remove ICs. These signals all go to
one row of pins of a 64 pin DIN 41612 socket. The other row of pins is
wired ot the 32 pins of a ZIF socket.