Re: 2764 -> 2364/68764 adapter

From: Jim Brain <>
Date: Wed, 13 Jul 2016 12:12:18 -0500
Message-ID: <>
On 7/13/2016 11:30 AM, smf wrote:
> On 13/07/2016 13:48, Gerrit Heitsch wrote:
>> In man circuits they control the EPROM through _OE and tie _CE to GND 
>> since that allows you to get away with slower EPROMs. This way the 
>> EPROM is always aktive and decoding addresses, just the output 
>> buffers are disabled. So you can hide quite a bit of the access time 
>> inside the delay for the decoder that selects the EPROM. Downside: 
>> higher power consumption with the old NMOS types. Doesn't really 
>> matter with CMOS.
> Exactly, which is why I suggested hooking up to _CE and using a 
> buffer. I am assuming that anything with a 2364 pinout is going to be 
> the same speed or slower than something with a 2764 pinout.
I think you have it backwards.  the OP wants to put a 2364 into a 2764 
socket, so the 2364 could be much slower than the original socket expects.
> If the 2364 you are using is actually powered up all the time decoding 
> addresses and the _CE only turns on the output buffers 
_CE does not turn on output buffers.  _CE is chip select.  _OE turns on 
output buffers
> then you could get away with just checking for (_CE | _OR ) == 0.
You can do so, but that costs an OR gate, and most times, 2764 sockets 
just tied CE to ground all the time, as the power savings with CE =1 
would not matter.

In any case, the PCB in my store attaches _OE of the 2764 socket to _CS 
of the 2364.  If your 2764 does the same, you're done.  If it uses _CE 
to trigger (which I have not seen), cut the trace and jumper.  If it 
uses both (which I have seen, though rarely), It's OR gate time.  If you 
deadbug the IC, you can stash it in the interior of the 24 pin socket, 
as you only need 5 connections (A,B,Y,PWR,GND)


Jim Brain

       Message was sent through the cbm-hackers mailing list
Received on 2016-07-13 18:00:02

Archive generated by hypermail 2.2.0.