22-08-2021, 02:20 AM
PAK5 should be called SHELL not MENU as there is a separate MENU ROM used in the PC85b, this ROM actually resides at PAK 10 position.
So even if you do hid correct decoding you can't access ROM 10 as it is reserved for the MENU ROM.
That's the reason the "PC85b eprom IC27 (PAK 5, aka the SHELL)" crashes is that it tries to switch in the MENU at PAK 10 position and doesn't find it there.
That all said as Chickenman stated, there is two versions the PC85 and the PC85b.
The PC85 can only address PAK ROMs 0 - 7. PC85B adds and extra data line to the HCF4042 Latch and this latched output is used to bank switch the PAKs to decode ROM PAKs 8 - 15.
The board revision that enabled this was Rev 6, you have the Rev 4 board, but still doable if required.
However I would get it working in it's present form first before launching into any upgrading.
Ernest
So even if you do hid correct decoding you can't access ROM 10 as it is reserved for the MENU ROM.
That's the reason the "PC85b eprom IC27 (PAK 5, aka the SHELL)" crashes is that it tries to switch in the MENU at PAK 10 position and doesn't find it there.
That all said as Chickenman stated, there is two versions the PC85 and the PC85b.
The PC85 can only address PAK ROMs 0 - 7. PC85B adds and extra data line to the HCF4042 Latch and this latched output is used to bank switch the PAKs to decode ROM PAKs 8 - 15.
The board revision that enabled this was Rev 6, you have the Rev 4 board, but still doable if required.
However I would get it working in it's present form first before launching into any upgrading.
Ernest