People, very sorry for the OT, but the info may be of interest of anyone
in this list, since we are all involved in electronics, and this is an
usefull tool.
> You did an eprom emulator? How well does it work? I've been thinking
about
> building something of the sort, probably wire-wrapped (unless you want to
> sell a board :-), and have heard of people having problems with signal
> quality if it's over any nontrivial distance.
> How big of an eprom are you trying to emulate? I'm not particularly
ambitious
> in that regard, but do have a bunch of 8-bit parts I'd like to see some
use
> for.
Ok, lets see what an eprom emulator is: A bunch of memory, a counter and
a buffer.
My eprom emulator emulates up to 27C080 (1 Megabyte) and can be expanded
to 2 megabytes easily, adding another memory board (and my God, how much
power will it use!).
My emulator has two boards: Memory board and counter board.
The memory board is nothing besides 32 x 32k x 8 cache SRAMs taken from
486 motherboards. Even the high-quality sockets on that!!! Also, some LS'138
for adress decoding. It takes the five top adress lines, and generates CS0
to CS31 lines. Ah, one '04 and some glue logic. You can find it on the
www.onsemi.com in the ttl data book, I use exactly the same schematic of the
demo of the '138
On the counter board, I just use an Atmega 8515, aderessing the entire
block of RAM as if it were "windows" of 32K. So I can use al the internal
commands of the AVR for external memory, and five more bits for selection of
the 0 to 31 memory bank. So I can download the code thru the serial (why
serial? Because it is EASY to implement and I can use it without any kind of
program, uploading the data with xmodem or doing adress=value and changing
it in real time. Maybe in the future I can implement an ANSI hex/ascii
memory editor) and store it on the RAMs.
After downloaded, some '245 reconnects the entire memory board to the
EPROM socket, and a transistor resets the circuit
I think that with this explanation, anyone can build your own EPROM
emulator .
Want to do a SIMPLER eprom emulator????
Use the parallel port. D0-D7 to send data. One pin sends RESET to a
bunch of cascaded 4040 (binary counters? I'm telling from memory) and
another sends clock to the same bunch. On the end, you use the same 245 to
reconnect the data/adress bus to the memory socket. Simpler, but no real
time trace/update :o)
Greetings,
Alexandre from Brazil
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