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Serial communications over 2 wires?

N

news.valornet.com

Jan 1, 1970
0
Hi,

I have a diagnostic tool that records information. It has some sort of a
proprietary interface port on it, just 2 conductors. I can tell one of them
is ground. The remote that normally hooks to this interface port has some
sort of two way communicatoin with the diagnostic tool. It can send
commands to the tool, but mostly the remote outputs to a serial device at a
very slow speed. I would prefer not to have to purchase the remote device
and make my own so that can get information from the diagnostic tool. I
wonder if the tool itself outputs in serial and I just need to hook up to
it.

Can the RX and TX pins in a serial interface be combined to a single pin
somehow? I really expected to find 3 conductors.

Is there any way of using a DMM to find out if the 2 conductors (one ground)
is a serial interface? The resistance between them is about 4.7k. I don't
see any voltage on them.

How could/would communication like this occur over 2 conductors that
involves slow serial (1200 baud)?

TIA!
 
L

Luhan

Jan 1, 1970
0
news.valornet.com said:
Hi,

I have a diagnostic tool that records information. It has some sort of a
proprietary interface port on it, just 2 conductors. I can tell one of them
is ground. The remote that normally hooks to this interface port has some
sort of two way communicatoin with the diagnostic tool. It can send
commands to the tool, but mostly the remote outputs to a serial device at a
very slow speed. I would prefer not to have to purchase the remote device
and make my own so that can get information from the diagnostic tool. I
wonder if the tool itself outputs in serial and I just need to hook up to
it.

Can the RX and TX pins in a serial interface be combined to a single pin
somehow? I really expected to find 3 conductors.

Is there any way of using a DMM to find out if the 2 conductors (one ground)
is a serial interface? The resistance between them is about 4.7k. I don't
see any voltage on them.

How could/would communication like this occur over 2 conductors that
involves slow serial (1200 baud)?


Easy, open-collector drivers (or Tri-States) at both ends. This is
assuming one conductor is a ground.

Otherwise, 2 wires makes a current loop with both sending and receiving
at both ends.

Luhan
 
R

Roger Hamlett

Jan 1, 1970
0
news.valornet.com said:
Hi,

I have a diagnostic tool that records information. It has some sort of
a proprietary interface port on it, just 2 conductors. I can tell one
of them is ground. The remote that normally hooks to this interface
port has some sort of two way communicatoin with the diagnostic tool.
It can send commands to the tool, but mostly the remote outputs to a
serial device at a very slow speed. I would prefer not to have to
purchase the remote device and make my own so that can get information
from the diagnostic tool. I wonder if the tool itself outputs in serial
and I just need to hook up to it.

Can the RX and TX pins in a serial interface be combined to a single pin
somehow? I really expected to find 3 conductors.

Is there any way of using a DMM to find out if the 2 conductors (one
ground) is a serial interface? The resistance between them is about
4.7k. I don't see any voltage on them.

How could/would communication like this occur over 2 conductors that
involves slow serial (1200 baud)?

TIA!
Visit the Maxim/Dallas web site, and have a look at their '1 wire bus'.
Really a misnomer, since there has to be a second 0v connection to
complete the circuit, but one a single 'signalling' wire, which can carry
power as well. Quite a lot of things like weather station senders etc.,
use this interface.

Best Wishes
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
news.valornet.com said:
Hi,

I have a diagnostic tool that records information. It has some sort of a
proprietary interface port on it, just 2 conductors. I can tell one of them
is ground. The remote that normally hooks to this interface port has some
sort of two way communicatoin with the diagnostic tool. It can send
commands to the tool, but mostly the remote outputs to a serial device at a
very slow speed. I would prefer not to have to purchase the remote device
and make my own so that can get information from the diagnostic tool. I
wonder if the tool itself outputs in serial and I just need to hook up to
it.

Can the RX and TX pins in a serial interface be combined to a single pin
somehow? I really expected to find 3 conductors.

Yes. As someone else stated, using open collector drivers is one
technique.
Is there any way of using a DMM to find out if the 2 conductors (one ground)
is a serial interface? The resistance between them is about 4.7k. I don't
see any voltage on them.

Better to use an oscilloscope. A DMM might be able to detect a longer
message. Put it in AC mode and try. But if it has a slow response time,
you're likely to miss the signal.
How could/would communication like this occur over 2 conductors that
involves slow serial (1200 baud)?

The communications protocol includes commands for reversing the data
direction. Or certain commands are structured so that the master prompts
the slave to reply and then listens for a certain amount of time.

--
Paul Hovnanian mailto:p[email protected]
------------------------------------------------------------------
100 buckets of bits on the bus
100 buckets of bits
You take one down,
and short it to ground
FF buckets of bits on the bus
 
J

Jamie

Jan 1, 1970
0
news.valornet.com said:
Hi,

I have a diagnostic tool that records information. It has some sort of a
proprietary interface port on it, just 2 conductors. I can tell one of them
is ground. The remote that normally hooks to this interface port has some
sort of two way communicatoin with the diagnostic tool. It can send
commands to the tool, but mostly the remote outputs to a serial device at a
very slow speed. I would prefer not to have to purchase the remote device
and make my own so that can get information from the diagnostic tool. I
wonder if the tool itself outputs in serial and I just need to hook up to
it.

Can the RX and TX pins in a serial interface be combined to a single pin
somehow? I really expected to find 3 conductors.

Is there any way of using a DMM to find out if the 2 conductors (one ground)
is a serial interface? The resistance between them is about 4.7k. I don't
see any voltage on them.

How could/would communication like this occur over 2 conductors that
involves slow serial (1200 baud)?

TIA!
i think your talking about open collector Txing ? that is where you
can tie the TX over to the RX via an open collector from the TX side.
its a single wire (with common) form of bi-directional serial.
 
D

delo

Jan 1, 1970
0
The videocamera LANC interface work with ground and only one
signal with open collector.
To find the common - gnd pin (if you ave access to internal circuit
or the common of power supply, or the negative terminal of a battery),
try the continuity with one of the two pin You have, You MUST use
a continuity tester with a negligible ddp (continuity tester) not a
normal multimeter wich put too much voltage on the tested circuit.
Such testing device is quite useful to deenginnerig a board without
damaging it, and can be built with a simple lm393 and 6 resitors.
In MHO the scope is a must You must measure the level of "one".
In the case of oc if the pull up is on the device when the line is idle
You can measure about Vsupply, different case if You are in presence
of 1wire interface, btw if you have access to the inside You can figure
out wath kind of interface chip is placed in.

bye
delo
 
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