Communication problem between javacs and Basic Stamp(sx) via RS232

[J.We]

I am trying to send commands from a java program (using javacs.comm, java extension communications) to my BSsx. The bauds are off course set to the same on both side. 8-bits, no parity, 9600 b-rate and so on. I have also tried on slower baud rates..
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The BSsx is programmed only to listen to the SERIN and GOSUB (drive a stepper motor via Little Step U), when receiving any data (one byte).
The java-program is programmed to locate the COM1, open it, and send one byte data, hold the port open five seconds, and then close the port.
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The BSsx program work fine when using a terminal–program (RealTerm), but not with the java-program, and the java program work fine separate to.
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Why is my system not working?
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Please see attached files, TestMain.java , SerialIO.java (java-files) and TestMain.bsx (basic stamp-file).
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Please, if anyone have done anything like this, please give me some advise! If anyone have any type of suggestion on haw to move on, don’t hesitate to reply this.
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Regards//jw

[Jon Williams]

The problem has to do -- I believe -- with what your Java program is doing to the DTR line; that line connects to the Stamp's ATN pin to cause a reset. Check the docs to see if you can change the DTR state.

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Jon Williams
Applications Engineer, Parallax

[Dave T]

I am also interested in the resolution of this problem since I am also trying to use java libraries to communicate. So far the solution has been to have two serial cables--one with pin 4 removed physically--and one normal. I have to swap the cables each time I want to switch from programming the basic stamp to running my PC program to communicate with the stamp. I know there have been suggestions to insert a jumper or switch, but I wish there was a way to do it in software (i.e. in the Java code). i bet someone, somewhere has resolved this issue and I just need to find where the explanation is!!

[allanlane5]

Don't close the port in Java. When you open the port, the PC hardware turns 'on' DTR and holds it on. This 'blips' the ATN line (due to a couple of capacitors) which resets the BS2. If you don't close the port, you won't 'blip' the ATN line again.

I don't know if Java gives you the option of opening the port without letting the DTR line transition.

[Dave T]

Thank you for taking an interest in this issue. I am testing, but don't quite understand why not closing the port could help since all communication problems or successes are already done by the time the port would ordinarily be closed anyway. I don't yet see how to prevent DTR from being affected by opening the port.