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'[EE]: 2-wire comms Was Replace old chips ?'
2002\01\24@072305 by Jinx

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> Will there be an f628 in every remote clock too? How are you
> going to link them up?

No, just one or two F628s in the master. But if I needed to comm
with remote PICs I'd use a two-wire 100 ohm twisted pair. This
is a simple technique for using a common ground and a 5V line
with the data superimposed on it. Much easier to find suitable
2-core wire than 3-core. Works very well

However, I can't use this circuit in this case. For one thing, the
job doesn't call for it.

In the circuit here, the 5V power has to come from the receiving
end. It's isolated and smoothed at, and for, the transmitter. Data
is sent to the base of the transistor, which causes blips on the
Vcc line (by momentarily shorting it) that can be picked up by the
receiver. The receiver's Vcc should be buffered by a small cap
so it isn't reset

So has anyone bright ideas for 2-way 2-wire comms using the
Vcc line ?

I think there are still laughs to come with this job. Yet to find out
what type of clocks they have that can go backwards when they
adjust for local time


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part 3 131 bytes
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2002\01\24@113250 by Tom Messenger

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At 07:02 PM 1/24/02 +1300, you wrote:
>
>So has anyone bright ideas for 2-way 2-wire comms using the
>Vcc line ?

I've used 1-way 2-wire comms on 3 or 4 different products in the distant
past.  Correct me if I'm wrong but won't this work fine for half-duplex?
Each end of the link has to be in on the joke, of course. If not using a
polled method, then for async operation, you must do something to handle
collisions.  My first approach would probably be along the lines of
master/slave: don't talk until you get permission. Of course then, the
master must poll often enough to deal with all matters at hand.

>I think there are still laughs to come with this job.

That's why we are all in this vocation, isn't it? :)

>Yet to find out
>what type of clocks they have that can go backwards when they
>adjust for local time

Of course, you could take the other approach and pump then around forward
11 hours (or 23 hours if dealing with 24 hour clocks).

Good luck!
Tom M.

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2002\01\25@053827 by Jinx

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>         Russell McMahon

Some good suggestions

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2002\01\26@042759 by Peter L. Peres

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The oldest and best tried 2-wire comms with power is a telephone line. You
can signal using tones or interruptions (like pulse dial).

The easiest communication is using RS232 (inverted or not) at baseband (no
carrier).

If you need to update clocks with setting info you can send a short burst
at say 19200 once a second or once a minute.

The bidirectional part is handled by all the parties listening all the
time (including to its own tx). Thus a jammed transmission will be
detected and the sender can reschedule and retransmit it easily.

Peter

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2002\01\26@063451 by Russell McMahon

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Continuing the "strange ways to signal on 2 wires" theme, for the master,
you could swap line feed polarity as signalling. If slaves have full bridge
power pickup they get 100% power feed at full signalling rate.

In a loop you could extend this to slaves with each swapping power feed
polarity to downstream members until the loop got back to the master.

Polarity swpaiing has the advantages of no pwoer interuption and good speed.

_________

Versions of the 2 wire half duplex and 3 wire full duplex on power supply
wires were implemented by the old Nat Semi "AARTS" of the ?1970's The number
MM14469 (MC14469?) or similar rings a bell but this may be wrong. These
received an address and one or ? two data bytes and responded with a data
byte of their own. Processorless remote serial I/O. Quite easy to implement
with a modern processor.

Yep - just checked my heap database - it is MC14469. Price here was $NZ13.50
in 100s in 1992 so a PIC would easily get under that.



   Russell McMahon

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