Wang 720 ROM
Reading and Recovering Microcode
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, it will need further investigation and perhaps re-trimming of component values to compensate for drift over the past fifty years.
In the meantime a ROM emulator will be used to continue the restoration of the main machine.
