Re: 6502 illegal opcodes questions

[Linards Ticmanis <ticmanis@gmx.de>]

Paul Schlyter wrote:

> Using soft interrupts as entry points on the Apple II would have been
> infeasible -- but Apple could have used a JMP table instead, positioned
> near the beginning or the end of the ROM address space.  CP/M used that
> method for entry points to its BIOS: a series of JMP operations at the
> very beginning of the memory block used by the CP/M BIOS.

Commodore did the same by the way; they have that "kernal" jump table at
the end of the ROMs which stayed fairly stable throughout their 8-bit
line, and which is easy to "hook" since most of the important entry
points use indirect JMPs through a RAM vector. Didn't actually make the
machines very compatible with each other, though.

-- 
Linards Ticmanis