RAM used as EPROM - pseudo 2732

RAM used as EPROM As long ago as December 1981, we acquainted you with an easily programmed replacement for the 2716 EPROM: the IPROM. In September 1984, we introduced you to MOSTEK"s 48Z02, which is compatible to both the 6116 RAM and the 2716 EPROM. It is now time to make you familiar with a replacement for the widely used type 2732 EPROM, consisting of two battery buffered 2 Kbyte RAMs type 6116, which can simply be inserted into the available EPROM socket. With a small additional extension, the circuit can also be used as a substitute for the less common type 2532 EPROM. As regards terminals A11 and CS of the EPROM socket, it is essential that the cor- rect pin of both 6116s is connected to these, and this is ensured by a 2-bit binary decoder in IC3. Pin 3 of IC3 is at earth potential when the power to the computer is on, and this enables the decoder. The truth table for this situation is given in table 1. Of interest are the situations in which the CS line goes low. If addres...