6 Jan
2012
6 Jan
'12
2:15 a.m.
James Attfield wrote:
My sloppy work, apologies, I was referring to the top bank of the memory
cards - the top 32K of a 64KZ will remain disabled until RDOS has relocated
itself during boot or test sequences then it switches it back in.
Ignore comment about port 40H - that is used for bank switching in 8-bit
systems.
Jim
FYI the ROM on the 'FDC flips in and out the entire top 32K bank.
I just double checked the schematics and this is not correct.
The 16FDC feeds address lines 15-12 through a 74ls30 to do a
specific decode for a 4K address range, normally set to $C000-$CFFF.
If the high four address bits do not match, the card will not
respond.
Bill S.