<>A Z80 will give useful patterns executing continual 00 (NOP, so the
<>address bus cycles through all of memory) or FF (RST 38, so the stack
<>builds down to fill all off memory). Both should provide useful patterns
<>on DRAM control lines.
<>
<Of course, the old IMSAI didn't have a Z80, though I imagine the behavior o
<the 8080 is similarly predicable to some extent. However, this puts us in
<the realm of "coulda-woulda-shoulda" which is not where I like to work. A
<prom is easy, quick and earseable. If you don't have a few for diagnostic
<purposes, you get what you deserve.
same as z80 case, plus the front pannel can be very useful. However,
your point make two assumptions, a prom card or a card that assumably
works and takes a prom and the tools to program that specific prom.
When I was doing most of this stuff alot (early 1973-1983) those things
were often in short supply or non existant and a LA was stratosphere
priced.
<I guess I'm stupider than average, but I have never found what I get from
<logic probe to be particularly useful, nor have I gotten reliable/repeatabl
Different style and presentation. With a LP you attack section by section
and you have to visualize the big picture.
<results. The 'scope doesn't lie, however, and once you own one, it's a
<mistake even to pick up the logic probe, since it can tell you so little.
Wrong. I have all three and they have their place. Often the LP
is more than enough. It was enough to shoot the PDP-8f front pannel
with a bad input 7451 (lots of inputs!) and without a print!
<The logic analyzer is quite a complex beast and requires experience and
<patience to set it up and to utilize the information you get from it
<correctly. The reason I'm using mine is because I'm building a bus probe
<for the S-100 to be run from a PC. This will simulate a front panel on th
<screen and (hopefully) trivialize the task of making individual boards in
<the S-100 cardcage "so something" to aid in trouble-shooting. I'm not far
<along yet, but I thing taking a few pictures of the significant waveforms
<while fiddling with different CPU cards will get me back into the swing of
<things.
I found an easier way. Netronics 8085 system. 8085 with prom, ram, IO
local to itself and a s100 extension off that. Bought it in '78 before the
lightining hit fried the altair and it was vey useful as even dead cards
could be driven. Some of the S100 SBC style CPUs (Computime SB880 come to
mind as I have one) is also useful as it has z80, serial, 1kram, eprom
all on the card and great for driving the deadest of s100 busses.
<Some magazine published a multiplexer for the oscilloscope which enabled a
<externally triggered 'scope to display 8 multiplexed channels in either
<alternating or chopped mode. That was about 20 years ago, but little
<gadgets like that cost only a few bucks to build and will save lots of tim
<on things with several interacting signals. This one used 4000-series CMO
<stuff to form a bias voltage be summed with the logic signal in order to
Built one. Too slow to be useful for logic of even 8080 speeds. the
4066s were barely good to 10mhz as the board was laid out.
Allison
Received on Wed Jun 02 1999 - 19:26:56 BST