Re: RAM replacements

From: Gerrit Heitsch <>
Date: Wed, 12 Sep 2012 19:34:24 +0200
Message-ID: <>
On 09/12/2012 07:12 PM, wrote:
> Are there any indications against using eventually e. g. 128K of low power S-RAM for everything? I mean.. putting aside the mechanical complexity of the adapter required. 128Kx8 SRAMs seem to be easily available and far less expensive than a set of 4164s (or even 41464s) and 4114 these days. Where is the catch, if any?

There is a small one. I have built an adapter to use a 128K-SRAM 
(ALLIANCE AS6C10008-55) on a 250466. You need the RAM, a 74HCT573 as the 
demultiplexer and a single OR-gate (I used a 74LS32). The nice thing 
with an SRAM is, you can connect address and data lines in any order you 

The LE-signal for the 74HCT573 is connected to _RAS. The OR-Gate takes 
_RAS and _CAS as inputs and the output is the _CS signal for the SRAM. 
In theory, just _CAS should work, but it doesn't, the system crashes, 
possible due to _CAS being run through the PLA and _RAS going inactive 
before _CAS does.

With the OR-Gate the circuit works. I can run whatever I want, the board 
doesn't crash.

Now for the small catch... The SRAM uses so little power that it will 
not lose its contents if the C64 is powered off, but the floppy drive is 
still on. The current coming in through the pullups on the IEC is 
enough... In order to get around that, hook up a 10 Ohm resitor between 
GND and the power switch so that when the C64 is off, +5V and GND on the 
board are connected by 10 Ohm. This is done on the 250469 boards.


       Message was sent through the cbm-hackers mailing list
Received on 2012-09-12 18:00:23

Archive generated by hypermail 2.2.0.