21MX proms (per request)
jwest at classiccmp.org
Sun Sep 6 14:04:30 CDT 2015
The loader PROMs are 256x4 while the firmware PROMs are either 512x8 or 1024x8. The firmware has some interesting code to unpack the 256x4 loader PROMs into 64x16 format in memory, and patch in the I/O select code while it is doing it.
The same 1K parts are used interchangeably for loader roms or microcode on the FAB. They are the same chip regardless of if they contain loader code or microcode.
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