[Osborne] Dual BIOS ROM Daughterboard (2732->2764)

[clueless_engineer (Brett)]

Thanks to @nelgin making the alternative OZROM BIOS binary available from his machine, I designed a simple daughterboard so that both the original OCC BIOS and the OZROM BIOS can be installed at the same time, switchable via the A12 address pin.

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Seems to work okay. The RAM tester identified a fault in bank B (4000-7FFF), 4th bit, so I apparently need to change the chip in location B24.

 

[clueless_engineer (Brett)]

 

[clueless_engineer (Brett)]

As the ROM works, I've made a new daughterboard soldering the EPROM directly to it.