ROM BIOS of the Plus Hardcard 20 Version 3.31 (1986)
This card has a single 64k BIOS chip. Chip marked "B33" See Picture.

Original EPROM M5M2764P located in socket U115


Image source: TOP853 Programmer

File Name: HC20U115.BIN

File Size: 8,192


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There is a D27128C socketed chip on this board at location U114 that is included.
Chip marked "F34" See Picture.

Original EPROM D27128C

File Name: HC20U114.BIN

