On Wed, 1 Feb 2012 16:17:52 -0500 Bill Freeman <ke1g...@gmail.com> wrote:
> If I recall correctly, the Apple ][ bus gave us ROM on the I/O card to > bring the driver with the hardware, but addressing was controlled by > which slot you put the card in, and the signalling was closer to buffered > 6502 signals, rather than buffered 8088 signals. So I don't see that > as being any more of a forerunner of ISA than S-100 was. Hi everybody, I've been lurking on the discussion... Yes, the 6502 had memory-mapped I/O only, so it was much different than 8080/x86. The instruction set didn't have any I/O instructions at all, you just wrote to an address that was pre-defined by the computer's architechure as I/O. On the Apple II, all the I/O was in C000-CFFF. Somewhere within that space (I forget where) each of the eight slots had 16 bytes, selected by a pair of 74LS138's on the motherboard. If you wrote (or read) to one those addresses, you were talking to one of the I/O slots. It was up to the card/driver as to which of those 16 were control or I/O or whatever. Any card could pull down an inhibit-select to disable the ROM on the motherboard and run its own stuff. Ron Smith r...@mrt4.com ps- I'm sorry if you got 2 of this email, first attempt failed. _______________________________________________ gnhlug-discuss mailing list gnhlug-discuss@mail.gnhlug.org http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
