The only non-protected board that can bankswitch and use all V ROM space. Really common and very useful for homebrew stuff or converts.
Often used as the PROG board in Neo Print cartridges.
P ROMs configuration
EP ROMs /OE
P2 ROM /CE
P2 ROM /OE
|/ROMOE||/PORTOE (default)||/PORTOE, banks 0 and 1|
P1 ROM /OE
|/PORTOE||/PORTOE AND /ROMOE||/ROMOE (default)||/PORTOE, banks 2 and 3|
P1 ROM /CE
P1 ROM size
|A19/NC is /PORTADRS (P1 is 16Mbit)||A19/NC is BANK0 (because reasons?)||P1 is 8Mbit|
P2 ROM size
|A20//BYTE is VCC (P2 is 16Mbit or less)||A20//BYTE is BANK1 (P2 is 32Mbit)|
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.
V ROMs configuration
There is a maximum of 4 V ROMs which can be 8Mbit, 16Mbit or 32Mbit (27C800/27C160/27C322) 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).
|Largest V ROM||Jumper set|
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.
The LS08 is used to AND the /PORTOEU and /PORTOEL signals to get /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, LS74A