Dumping ROM combo chips

[Ludis Langens]

Many of the older GM ECMs use a 40 pin DIP combination ROM/RAM/IO chip. 
(The pinout is on my web site.)  This chip has 4K bytes of ROM, 128
bytes of RAM, and 8 digital I/O lines.  The chip receives all 16
processor address lines and does it's own address decoding.

If you wish to read out the ROM from one of these out of circuit, you'll
need to provide an E clock signal.  I wired up an adapter to read these
chips in a PROM reader as a 27512.  The RAM and I/O appear to read OK
with E tied high.  The ROM however doesn't.  The PROM ~OE signal needed
to be inverted and applied to the combo chip's E input.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/