On Wed, Feb 1, 2012 at 9:59 PM, <r...@mrt4.com> wrote:
> 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 > > FWIW, the 6502 is once again available for purchase. The original masks were lost, but someone opened up an old 6502, took out a microscope...
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