Memory map

I/O ports related to bank switching

Memory bankAssociated I/O ports
Expanded RAME2h: Bit 4, 0 Read/Write enabled
E3h: Bank selection
EROM (4th ROM)31h: Bit 2 (RMODE = 0)
31h: Bit 1 (MMODE = 0)
71h: Bit 0 (IEROM = 0)
32h: Bit [1:0] (EROMSL) Bank selection
N88-BASIC ROM31h: Bit 2 (RMODE = 0)
31h: Bit 1 (MMODE = 0)
N-BASIC ROM31h: Bit 2 (RMODE = 1)
31h: Bit 1 (MMODE = 0)
Main RAM31h: Bit 1 (MMODE = 1)
GVRAM5Ch, 5Dh, 5Eh: in independent access mode
35h: Bit 7 (GAM = 1) In extended access mode
High speed TVRAM32h: Bit 4 (TMODE = 0)

When ROM is selected from 0000h to 7FFFh, writing into this range of addresses is done to main RAM.

Text window

Text window is valid when RMODE == 0 (port 31h: Bit 2) and MMODE == 0 (port 31h: Bit 1)

The contents of main RAM within 1K byte from the address whose upper byte is the value written to port 70h can be accessed through the text window.

When the text window is disabled, the main RAM (8000h to 83FFh) is visible as is.