PROGBK1

The only non-protected board that can bankswitch and use all V ROM space. Really common and very useful for homebrew stuff or converts.

P ROMs


The P1 ROM can be 4Mbit, 8Mbit or 16Mbit (27C400/27C800/27C160).
 * ROMs can be halved and mapped to 0x000000~0x0FFFFF or 0x200000~0x2FFFFF.
 * If P1 is 4Mbit or 8Mbit, then P2 can contain a bankswitched ROM (same type as P1 plus 27C322). P1 appears in 0x000000~0x0FFFFF. P2 bank appears in 0x200000~0x2FFFFF.

Bankswitching is done with the LS74. It's not needed if the game isn't banked. Any write to an odd address in the 0x200000~0x2FFFFF range will set the bank.

V ROM


There is a maximum of 4 V ROMs which can be 8Mbit, 16Mbit or 32Mbit (27C800/27C160) for a maximum total size of 4 * 4MiB = 16MiB.

A 4Mbit ROM can also be used, but only if there's one and only if it's in the last used slot.

The size of the largest V ROM is selected with a pair of jumpers on 6 spots (3 possible choices).

This pair of V ROM jumpers effectively choose a set of 2 of the PCM chip address outputs to input to the LS139, which will enable one out of the 4 V ROMs at a time.

The JV7 to JV14 jumpers need to be set according to the ROM types. If it's less than 32Mbit, the JV7/JV8/JV9/JV10 jumper needs to be set (ground). If it's 32Mbit, the JV11/JV12/JV13/JV14 needs to be set (A20). This is because 32Mbit chips have their /BYTE pin replaced by A20.

Other
The LS08 is used to AND the /PORTOEU and /PORTOEL signals to get a /PORTOE.


 * 4x 1/2/4MiB V ROMs
 * 1/2MiB P1 ROM
 * 1/2/4MiB P2 ROM
 * 2x 512KiB EP1/EP2 ROM
 * PCM chip
 * LS139,LS08,LS74