14 Jul
2010
14 Jul
'10
8:27 p.m.
On 14.07.10 19:59, Henk Gooijen wrote:
Jup. I was indeed thinking of byte-wide SRAM and EPROM (27512).
To keep things simple (and code efficient / fast) the EPROM will sit
in $FFFF0000-$FFFFFFFF (you need some ROM there for the reset
vector) and the RAM sits at $00000000-$0000FFFF. If you know the
68000, those 2 regions are "zero page" and references are shorter
which means less code bytes and less clock cycles.
I thought all interrupt vectors started from address 0. What do you need
A23 and the high addresses for?
I've read about designs that map ROM to $00 on boot to load stack
pointer etc. and remap to RAM later on to allow the user program to
modify the interrupt vectors.
How do I know then to remap the memory? I'd imagine it's done by the
monitor program, but I seem to recall that it was a hardware-only
solution. Have to find the article (German c't magazine's "Kat-CE" I
think it is).
Also, are there any grave disadvantages in leaving the ROM at address
$00 and using a jump table in RAM for the interrupts?
I am getting more and more tempted to try and built my own 68k SBC.
Being born in '84 it seems I missed out on all the interesting computers...
Sebastian