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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Tue, 13 Aug 1996 07:05:37 GMT
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Original-From:
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Brian Lavery <blavery@acslink.aone{StopSpammers}.net.au>
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Viewed:
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1427 times
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********************************************************
* (More) *
* MUSINGS ON THE SUBJECT OF HANDYBOARD INTERFACING *
********************************************************
* Multiplexed digital I/O *
* Sharing those valuable IC and OC pins *
********************************************************
Expanding a "clever" handyboard I/O line (an IC or OC or PA I/O)
into several time-multiplexed jobs:
|---------|
OC -->|D 237 |-->
| |--> 8 outputs - Identical to the
| |--> "High Overhead Servo"
|------ |--> circuit earlier
Y22 -->|Clk | |-->
A2 -->| | |-->
A1 -->| Addr| |-->
A0 -->|latch| |-->
|-----|---|
Note the CS could be ANY
useful one (even wrong
READ versus WRITE!) just
|---------| to get the address latched.
IC <--| 354 |<--
| |<--
| |<--
|------ |<-- 8 inputs time multiplexed
Y32 -->|Clk | |<--
A2 -->| | |<--
A1 -->| Addr| |<-- The 354 may be
A0 -->|latch| |<-- real hard to find !!
|-----|---| Solution: Use latched "address"
lines, eg from 8255, like below.
Sample uses of multiplexed I/O:
- slow async I/O (eg to Mini-SSC? - can we get it fast enough??)
- timing gate(s) for ultrasonic output(s)
- window for receiving ultrasonic echo(s)
- speed sampling from wheel encoders
|---------|
OC -->| 238 |-->
| |--> 8 outputs
| |-->
| |--> If you cant find HC237,
| |--> use this HC238 unlatched
X2 -->| a2 |--> method.
X1 -->| a1 |-->
X0 -->| a0 |--> The X0 - X2 are 3 latched
|-----|---| digital I/O from somewhere
else - eg 8255. They form
the addressing for the 238.
Bye again
Brian
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