Accessing partitions in drive images

[r270 at mrt4.com]

On Wed, 1 Feb 2012 16:17:52 -0500
Bill Freeman <ke1g.nh at 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
r270 at mrt4.com

ps- I'm sorry if you got 2 of this email, first attempt failed.