> 5) An
EPROM Emulator. I put this under test equipment because it's very
I need to
build one of these sometime. In the meantime, jamming a NOP on the
data bus when practical is often useful. I troubleshot a z80-based board
that way by removing one buffer chip and tack-soldering a bit of wire across
the bus pins, and watched the address lines cycle through the address space.
A bit more difficult with some other chips, but...
A not quite as handy alternative is to use one of the Dallas battery backedup
RAMs - easy to adapt it to an EPROM socket, and equally easy to build a
"programmer" (you just need a writable RAM socket on some piece of
equipment that you can easily download to). - Like an EPROM you still
gotta take it out and reprogramm it, but unlike an eprom, there is no erase
time and programming is virtually instantanious.
I also have a
little "clock generator" I put together which has DIP
switches to set the frequency and generates square waves - occationally it
has been very useful to clock a circult at a certain rate - often to slow
down "fast" stuff so I can see what it's doing.
What sort of rates do you find most useful? Sounds to me like this would be
easy enough to build.
It's VERY simple - basically, it's 3 LS163s two of which make up a programmable
divider, and one which is an output stage. The base divider gives me from 4.0 Mhz
to about 31Khz in 255 steps, and the output stage gives me /1 /2 /4 and /8 from
that output - so it can go down to about 4 khz.
I originally built it to go with "PCLA", a PC based logic analyser that I wrote
- captures
13 channels directly from the parallel port, however it can only go to about a 500khz
sample rate (depending on the PC) - which is basically as fast as you can do back to
back reads of the parallel port Too slow for most stuff, but by using the clock
generator,
I could slow a lot of stuff to be easily within it's range. Obviously there are
limitations
which is why I eventually replaced it with a "real" LA - but the clock generator
has
proven handy on other occations - but they are relatively few and far between.
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools:
www.dunfield.com
com Collector of vintage computing equipment:
http://www.parse.com/~ddunfield/museum/index.html
