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Problem When Hooking RS232 Through A Y-Adapter ?

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iso9001

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3 devices that need to talk to each other. A computer, a Device, and a monitoring tool. They all use just 1 wire via somthing close to RS232 to communicate (actually Motorolla SCI). Where the device has a 5V pullup and so does my monitoring tool, the computer floats and apparently can also pull high when it wants to communicate. It appears that by default the computer is in listening mode (?)

When I have the computer and either the tool or device plugged in everything works perfectly. My problem is that when I have the device and computer plugged and then plug in the monitoring tool, the devices immediately stops reporting data.

I can only assume this is a hardware conflict since I have not even set the tool to do anything.

My first idea is to maybe take the pullup out of the tool and then it cant only listen, but maybe thats a bad idea ?

Is this a common problem? Or anyway around it ?
 
You do not state what the "device" is, it may be helpfull to know.

You state the there is "one wire" in the comms link between the computer and device, I guess that there is a second wire making a return path somewhere, one wire does not make a circuit.

I had never heared of SCI until I read your post. A quick look with Google infers that is an old Motorola name for a device which the rest of the world calls a UART.

However, what we need to find out is:

1/ does the computer interrogate the device and the wait for a reply,
or
2/ does the device just send data to the computer?

also what is the function of the "Test Tool", is it intended to monitor the comms between the device and the computer, or is it a simulator to test the computer in the absence of the device?


If both the device and the test tool are trying to transmit at the same time, it will not work.

JimB
 
Yes, your question is far too vague?.

But basically you 'should' be OK with one TX and two RX, with communication from the single TX to both RX's - and nothing else!.
 
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