Jim Brain brain at jbrain.com
Fri Jan 2 00:38:58 CST 2009

Tony Duell wrote:
>>> 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.
> ... 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.
> 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 Brain, Brain Innovations                                      (X)
brain at jbrain.com 
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times! 
Home: http://www.jbrain.com

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