2 Jan
2009
2 Jan
'09
6:38 a.m.
Tony Duell wrote:
... except skiing through a revolving door :-)
More seriously, there must be a limit to the code size.
The unit I am using has 128kB of space, of which I am using 4kB for a
bootloader and 51K so far for uIEC DOS. But, a HPIB/GPIB based unit can
dispense with things like D64 images and such, so I think there may be
plenty of room. There are provisions for 3 switch inputs, which could
be used for drive and interface selection. It *might* be possible to
load everything into one firmware image, but I think it'd be best to
keep the CBM/non-CBM stuff separate.
I don;t know how much firmware space you have, but it
would be nice if at
least Amigo and SS/80 could be fitted in together with a jumper/switch to
select between them. I'd also suggest some kind of configuration
switch-thingy to select the drive size -- some HP machines moan if the
drive is not the one they're expecting...
Anything is possible.
All signals are bidirectional (although, unless you
intend to be a
controller, you don't ened to be able to drive some of them). Some devices
drive them with totem-poll drivers, others open-collector (with passive
termination). There are arguements in favour of either for particular
applications.
-tony
I'm planning on OC outputs.
My idea is to make the ATA (IDE) interface do double duty. As I look at
the signal table for ATA, I notice a few unused states:
/CS0 & /CS1 = IEEE CS
A0 selects data or control lines
READ selects a read
WRITE selects a write
I'll probably use the 75160/75161 ($4.00 for SOIC, $2.80 for DIP for the
two ICs), though I prefer '245s for the inputs and TPIC6B273s for the
outputs. (3.40+.82 = 4.42 for the 4 ICs).
A single '138 should decode what I need from the IDE control signals.
Jim
--
Jim Brain, Brain Innovations (X)
brain at jbrain.com
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!
Home: http://www.jbrain.com