[Gmecm] Converting eprom to eeprom problem

[Mike Poore]

The 2732 access time is 200 ns and the 2864 is 120 ns. I assume faster 
is fine. There are two floating pins (1 and 26), which my data sheet 
shows as NC (No Connect). I do not have the bypass cap you mentioned. 
Can you explain the purpose and suggest a value? My intuition tells me 
there is a timing issue with Chip Enable. Here is the data sheet 
description of the read operation of the 2864:

The 28C64 is accessed like a static ram. When CE and OE are low and WE 
is high, the data is stored at the memory location determined by the 
address pins is asserted on the outputs. The outputs are put in a high 
impedance state whenever CE or OE is high. This dual line control gives 
designers increased flexibility in preventing bus contention.

I should point out that WE is connected to Vcc and CE and OE are 
connected to the 2732 CE and OE pin locations. The 2732 datasheet 
indicates data is available at the outputs after the falling edge OE. 
Could there be an issue where the A12 pin has not been low long enough 
or is transitioning at the point of reading data. If yes, can you 
suggest another source for a reliable low signal to apply to A12. Could 
I reduce voltage of Vcc to a low signal? If yes, can you tell me how?

Thanks, Mike

Darryl M Gilbert wrote:

>Hmmmmm, should work. Do you have a bypass cap between Vcc and gnd right
>at the chip?? I would have to look at the chip specs to see whats up, but
>sounds logical. Make sure when you switch from one to the other no pins
>are left floating, you know, not connected to anything. All pins should
>be terminated, never floating
>good luck
>darryl..
>On Tue, 04 Oct 2005 20:05:33 -0500 Mike Poore <mp at FlowersByValerie.com>
>writes:
>  
>
>>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
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>>Gmecm at diy-efi.org
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>>
>>
>>    
>>
>
>  
>
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