Serial communications over 2 wires?

Question

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!

Luhan · Accepted Answer

Easy, open-collector drivers (or Tri-States) at both ends.  This isassuming one conductor is a ground.Otherwise, 2 wires makes a current loop with both sending and receivingat both ends.Luhan

Roger Hamlett · Answer

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

Paul Hovnanian P.E. · Answer

Yes. As someone else stated, using open collector drivers is onetechnique. Better to use an oscilloscope. A DMM might be able to detect a longermessage. Put it in AC mode and try. But if it has a slow response time,you're likely to miss the signal. The communications protocol includes commands for reversing the datadirection. Or certain commands are structured so that the master promptsthe slave to reply and then listens for a certain amount of time.   -- Paul Hovnanian     mailto:------------------------------------------------------------------100 buckets of bits on the bus100 buckets of bits   You take one down,   and short it to groundFF buckets of bits on the bus

Jamie · Answer

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.

delo · Answer

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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marketing · Answer

Try to use DC power line communication. You can transfer both data andpower on the same wires. There are transceivers for speeds of 10Kbps to500Kbps. Try Taly. wrote:

Serial communications over 2 wires?

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