Reading and Recovering Microcode

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The ROM was removed for specific inspection and appeared to be undamaged. It is version P720-2A with an illegible date stamp.

The ROM has a series of ECNs applied to the sense transformer circuits, the latest of these are dated September 1971 in the schematics, so the ROM must date after that time. The ROM is labelled as version P720-2A and Wang documents note that this version should be replaced with 720-B1. Perhaps the -2A version has bugs?

This P720-2A ROM has 28 of a possible 32 rows of diodes populated, allowing a maximum of 1792 address wires to give a total capacity of 1792 x 43 = 77056 bits or 9.6k bytes.

Reading the ROM

DoPECC is keen to preserve the Wang microcodes and the DoPECC ROM reader can read Wang Wire Braid ROMs in a stand alone manner.

Attempts to read this ROM have not given stable results, this is in common with all the other wire ROMs that have been examined to date. Examination of the low-level ROM signals shows that data is present but sensing is inadequate. A future project will examine all the Wang wire ROMs in an effort to understand the mode(s) of failure and attempt full data recovery.

In the meantime a ROM emulator will be used to continue the restoration of the main machine.