31 Mar
2000
31 Mar
'00
1:26 a.m.
> The 3.5" square (exactly) daughter board
plugs directly into and
> only into where the Z80 CPU normally resides. The board contains:
> Z80 CPU, AM25LS252IPC, 2 x SN74LS245N, SN74LS00N, 74F32PC chips
> with assorted resistors etc. There is a 26 way berg connector to
> take the cable to the IEEE-488 port. Also there is a 8-way link
> box with 5 unbroken links, 2 broken links and 1 remade link.
I don't like to say things like this, but I think
I am justified...
'Impossible!'
You've got an address decoder (AM25LS2521 == 74LS688 IIRC), a
couple of bidirectional bus buffers ('245s), and a few gates ('00
NANDs and '32 ORs). What you don't have is any form of latch, which
is what you'd need for an output port. Since the IEEE-488 bus can
run a lot more slowly than the Z80 bus, it's going to need such
latches, at least for output. There are several possibilites.
Either you've missed out some chips (like '374s, or even a true
IEEE-488 chip like the 9914 or 7210). Or this is _not_ the IEEE-488
option. I suspect the latter, actually. I would be very suprised if
the RML IEE-488 option was a daughtercard that fitted under the
CPU. Everything I can find out about it suggests it's a normal Z50
bus card. This sounds like some kind of bus buffering/extension
card, sort of like the IDE interface (although obviously
incompatable with the PC type of IDE). Are you sure this is not
some kind of strange winchester interface. It could well be the
host adapter for (say) a WD1001 card or something like that.
Please feel free to say 'impossible' - my knowledge of electronics
at this level is minimal. I will now write out 100 times 'Failure
to pay due regard to warnings repeatedly given, brings in its train
dire consequences which might easily been avoided by the use of a
little self restraint' (school line). As you have pointed out
whatever this is, the person who installed it just made use of
the convenient sized hole marked IEEE port. Nothing which
came with the equipment (originally from Oxford University,
then from Biomechanical Engineering at UWCM (University of
Wales, College of Medicine), used that port.
Doug.