Subject:
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Musings regarding Handyboard Expansion & Interfacing
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 25 Aug 1996 08:35:44 GMT
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Original-From:
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Brian Lavery <blavery@acslink.aoneSAYNOTOSPAM.net.au>
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Viewed:
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1528 times
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Still idly thinking on future expansion possibilities for the H/B:
********************************************************
* MUSINGS ON THE SUBJECT OF HANDYBOARD INTERFACING *
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* Missing Expansion Interface signals *
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Note that the SPI connector seems to have two pins not used. Can we
patch the motherboard to feed extra signals to an expansion board system?
What signals should we choose?
------------------------------
- 40 kHz carrier of the H/B InfraRed system, so that it can be used
on an ultrasonic transducer? But many ultrasonic devices seem to
be at 37.x kHz or 39.x kHz or something else altogether. And 40kHz
can be generated again as needed.
- PA & IC1 & IC2? These are from the digital I/O bus, but JUST
outside the probable edge of an expansion board. So putting them on the
SPI connector gives easier access to exp board. But then, a small
plug on a flying wire could do the job at a pinch.
- HC11's "E" or "WR"? But the Y0-Y5 chip selects probably encapsulate
those enough for our needs. (Not sure - maybe a RAM design will need
these signals??)
- SCI async I/O? - could be a candidate, but then how would we easily
share that signal with the bootload operation?
- A0 - A1? These are useful for minor address selects on "big" chips.
But all of A0 - A7 are able to be regenerated fairly easily if needed
on an expansion board. The only thing that wants lots of the address
pins is Ram/Rom.
- System RESET? Would be good sometimes, but can probably be synthesised
by some output signal on the expansion system.
- INT / XINT? Having an interrupt pin available is really, really
useful for serious interfacing. INT can be used usefully by "smart"
additions
(another CPU or STAMP or PIC, compass EOC, 8255 I/O, UART chips, powerdown
detect, etc). But surely one of the other "smart" input pins (IC or PA)
already accessible to an interface expansion give us a defacto INT function
if we are clever enough.
- Address A10? - specifically to enlarge the size of one page of banked
expansion RAM to 2kB instead of 1kB. Also, it could help to subdivide
the Y0-Y5 chip selects into more pieces.
The wisest choice should be signals that:
- are not currently sent to any expansion point,
- and are not able to be regenerated,
- and could be very useful.
This looks to be our last chance to flesh out the expansion possibilities.
My vote:
========
I would like to put on some RAM, so I want signals for that. So I need to
do more homework to see if I need E / WR type signals - that would be a
pain. Otherwise if I dont need those, I will probable pick:
- 1. XINT (or INT)
- 2. Address A10
Anyone else with thoughts on good choice for the two free expansion pins?
Bye for now
Brian
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