8 Aug
2000
8 Aug
'00
5:34 a.m.
Hi, Eric!
I've gotten snippets of information regarding the IIc's I/O allocation
scheme. Does it support the constructs associated with the slots of
the ][+? I got out the ][+ doc's per your recommendation and looked at the
I/O allocation scheme, finding that each card was allocated 16 bytes of
memory map for local I/O. It also was allocated a page of memory for
device-unique code, ostensibly to initialize the device and condition the
system prior to enabling its on-board ROM if there was one. Is this same
memory allocated likewise in the IIc?
Which FDC bits would you recommend one use for parallel output? Having
looked at the ][+ FDC schematic, I find there are no directly controllable
output bits available, nor, in fact are there any directly accessible input
bits. Every otherwise conceivably available turns out to be attached to
something having other side-effects. This convinces me it would be simpler
to build an externally accessible channel, perhaps including power on its
own connector, or perhaps using the power available on the external FD
connector.
This has me leaning once again toward simply building in a channel similar
to what's used with the WD series bridge controllers. That's not because I
want to attach one of them, but rather because it's an easy interface
channel to use. It maps eight bytes under a single select and does so quite
simply. If one were to decode a card select, (12 bits of address, assuming
nothing about available decode signals for I/O and such, it would be easy
enough to time the write and read signals and buffer the 4 addresses that
remain. That would allow external decodeing of two 8-byte blocks,
sufficient for a PIA or some other general-purpose device, not to mention
discrete MSI components.
It's pretty simple to build a channel, since it doesn't require much logic,
and it's pretty simple to use it. What do you think? Since power is
available, there's no real reason to worry those same issues that make the
notebook less likely to provide a practical solution. I'd say the IIc and a
notebook provide pretty equivalent hardware solutions. Both require a
"brick" to operate for a longer period, though the notebook's is smaller,
(actually my Toshiba notebook didn't require one, but I gave that to my
elder son when he went away to college. The one I use now is a Winbook.)
and the size isn't an issue.
What do you think?
Dick