🚀 go-pugleaf

[In the message entitled "Re:  PC532 Expansion & other questions" on Nov 28, 18:03, randy hyde writes:]
> My board arrived.  Currently I'm pouring over the schematics before turning
> on the soldering iron.  I've got a couple of questions someone might be able
> to help me with.
> 
> 1) I note that the DUARTs live at ports 2800020, ...40, ...60, etc.  Yet the
>    address lines going into the 74138 imply that they should be at base
>    addresses ...10, ...20, ...30, etc.  Is the documentation correct?  If so,
>    is this an artifact of the decoding for the ICU?

The documentation is wrong. Hmm, why hasn't anyone else noticed this, every
just looking at the schematics?

> 2) I'm interested in a little off-board expansion without going through the
>    SCSI bus (I'm not ready to tackle the design of a smart SCSI controller).
>    I was thinking of popping off one of the DUARTs, running a couple of addit-
>    ional address lines (and unused decoding lines from the '138)
>    over to the socket and building a daughterboard to plug into
>    the DUART socket.  I'd like to put a couple of parallel ports
>    (perhaps a 6522 or 8255), an 8530 (I want to build an Appletalk
>    interface), and some other devices.  Any problems anyone can warn
>    me about?
> 
> 3) Along the lines of question 2, I'd like some additional interrupts.
>    can I cascade another ICU using the daughterboard technique des-
>    cribed above?

I suppose it should work. Have fun. Just make sure you don't run the
interface too far from the pc532. Even though the peripheral data bus is
buffered, it is still pretty fast.

On second thoughts, you will probably have trouble with timing. The 8530 is
real slow on the bus (last time I looked), and things like ancient 8255's
are probably even slower so you might have to jiggle with the wait pal to
get an extra wait state or so into the peripheral accesses - have more fun!

best regards,

-- 
George Scolaro (gs@vw25.chips.com)	Chips & Technologies
(408) 434-0600				3050 Zanker Road
					San Jose, CA  95134