[Gmecm] Converting eprom to eeprom problem

[Mike Poore]

I have an '870 ecm that has a 2732 eprom. My goal was to make a new 
board that I would allow me to use a 2864 eeprom. I have soldered in a 
new dip socket and remotely located the (e)eprom to a new board with dip 
switches to allow for using a 2732 or the 2864. The dip switches are 
configured to allow usage of the lower 32k or upper 32k of the 2864 
thereby tricking the ecm to think a 2732 is installed.

My theory is that if I could provide either a high or low signal to A12 
(pin 2 on the 2864), via the dip switches, then the ecm would address 
A0-A11 as normal. That would then allow the 2864 to be split into banks 
of 32k.

I have run tests and the 2732 works fine, so I know that there are no 
problems with noise or wiring of the circuit in this configuration. I 
copied the same bin to the lower half of the 2864. To provide high and 
low signals to A12 of the 2864 to read the 2864, I used Vcc (pin 24) of 
the 2732 socket connected to A11 (pin 2) of the 2864 to provide a high 
signal and used a low signal from Chip Enable (pin 18) of the 2732 socket.

Using the above circuit, the ecm works very briefly and then the ses 
light starts blinking very quickly, which seems to indicate a memory 
problem. That low signal from the Chip Enable circuit seems to be a problem.

Before going any further, can anyone offer an opinion as to wether the 
Chip Enable pin is a reliable low signal source, and if not, suggest a 
better way to get a low signal to A12. I have not tried using the upper 
32k yet, so I am also very interested in any opinions on using Vcc as a 
high signal for A12.

I am an electronics novice, so if you have a solution, please be 
detailed. For example, if you told me I need a pull-up resistor, I know 
the principle behind it, but could not figure out how to include it in 
my circuit. In other words, I know enough to be dangerous.

Thanks, Mike