M100ROM - 27C256 adapter for Tandy Model 100

The Tandy TRS-80 model 100/102 and 200 provide a ROM socket to add built in programs to the machine. To make inserting and replacing the ROM more user friendly the designers choose to use a custom chip socket (Molex series 78805) with 700mils pitch. The Molex carriers that mate with the sockets have been out of production for many years and are nowadays impossible to obtain. M100ROM is an adapter to use standard 27C256 EPROMs similar to the adapter originally used by PCSG to distribute their software.

Schematics

The schematics is trivial. All it is necessary is to map the custom pinout used by the Tandy to a standard EPROM. A single decoupling capacitor is also added to ensure good power integrity.