Apple IIgs Text mode doubled — #18

Post #18 by Elfen

Source Forum	68kMLA
Category	Troubleshooting
Post Date	Wed, 27 May 2015 - 04:09
Original URL	https://68kmla.org/bb/threads/apple-iigs-text-mode-doubled.2004/

Post

Pitou said:
@Gorgonops, ok thanks, will try that.

I have another question about the ROM chip. it's a 128kx8, so it needs 17 lines of addresses in order to access the entire memory of the rom. The 65SC816 processor seems to be a 24-bit address bus. So not a problem. However, by looking at schematic, only A0-A15 seems to be defined/implemented.

Also, if you look at page 9 of the PDF, the ROM chip, pin 22 (A16) connects to a resistor and goes to ROM output Enable?

Can someone confirm or explain the behavior here?

Thank you.

Pitou!

I believe that it is only using 64K of ROM instead of 128K. It can use it as bank switching use 64K for the Apple II+/e/c emulation, and the other 64K for IIgs.

Check if that line goes elsewhere, I bet it will.