January 11, 2019
The MOD_EMUP eprom burner - ISA card
As a first step towards reverse engineering this gadget,
I spent an evening working out the schematic for the ISA card
I have. My card is an SAC-201, which has switches along
with a GAL16V8 on the card.
A few weeks later I came across these resources:
The schematic was done by a fellow in Spain, Gonzalo Fernandez Val, for which I thank him very much.
Since the card he reverse engineered and drew has no GAL, but simply LS138 devices, it is easy to
understand the three mysterious signals the PAL generates.
The Cable
The protocol for the 25 pin cable is what is of most interest to me.
The 25 pins are as follows:
13 are power and ground
8 are a bidirectional data bus
4 are control signals
The control signals are as follows, all active low.
- pin 17 - Reset*
- pin 9 - Read port 2E2 -- Data port read
- pin 10 - Write port 2E0 -- ID port write
- pin 22 - Write port 2E2 -- Data port write
Pin 10 and 22 were "unknown A" and "unknown B" coming from the PAL on my board.
These were a mystery until I found Fernando's reverse engineering of the board without a PAL.
I misinterpreted pin 9 (since it also pulls low the DIR signal to the 245 chip
on a read). Except on that read, the DIR signal remains high.
There is a tremendous source of information in all03info.txt in the ALL03 software.
It details much of the protocol talking to the EMUP. In particular, it calls the
address 2E0 the "ID port" and 2E2 the "Data port". You select an 8 bit device in
the Emup by writting its address to the ID port, then read or write to it by
reading or writing the Data port.
Reading out the PAL would have been especially problematic given that I need the
MOD-EMUP to do so!! Not only that, when I received a MOD-EMUP A, which has a pair
of GAL16V8 devices inside, they had their security fuse set and could not be read
out. There is a good chance the GAL on the board would be this way also.
Have any comments? Questions?
Drop me a line!
Tom's Electronics pages / tom@mmto.org
