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TXD DTR Active
Dell Latitude running Windows 2000 (SP4)
The problem is that TXD and DTR on COM1 are active when the port is not in use. This is upsetting equipment that I plug into the serial port. How do I turn these signals off ?
flortep
114 Posts
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November 5th, 2003 22:00
R.H. what kind of equipment are you trying to connect ? Is there any adaptor : 25 -> 9 pin playing a role in that game ?
There's not much to say against DTR being active. It denotes that the "Data Terminal is Ready". The Data Terminal is your computer.
The equipment being connected is named "Data Set". The Data Set is a modem (by default from the old days) but could be a serial mouse, a pen tablet, a link to your PIM, a GPS sensor or anything better which talks as serial communication is supposed to talk.
The Data Set is supposed to "answer" the DTR signal from your computer with a "DSR" signal.
This tells your computer that the "Data Set is Ready" to communicate.
There is a second dialog starting when the computer wants to talk to the modem. This is RTS against CTS. Let's neglect that as of now, you'r stuck far before that goes on...
Of course you should have tested the basic functions of Com1 with Dells diagnostics, to make sure it's basically ok and working. Afterwards have a closer look to the connected device and have an even closer look to any 25 -> 9 pin adaptor as it might be wired the wrong way. Let me know the outcome...
flortep
Message Edited by flortep on 11-06-2003 01:13 AM
R.H.
2 Posts
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November 6th, 2003 03:00
The equipment and serial port work fine, The equipment just does not like the permanent break signal on the Txd line and DTR active.
The break signal on the Txd line goes once an appliction opens the port.
I have resolved the problem by using a USB->RS232 adaptor.
The problem seems to be a quirk with the Dell, I check other machines and Txd and DTR where inactive when the port has not been opened. For some reason Dell asserts Txd (permanent break signal) and DTR when the port is not used by an application.
I am still interested to find out why Dell asserts these signals and if they can be turned off by modifing registry settings or by other means.
flortep
114 Posts
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November 6th, 2003 06:00
sorry, finger trouble...
Message Edited by flortep on 11-06-2003 09:33 AM
flortep
114 Posts
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November 6th, 2003 06:00
R.H., I'll try that out with both a (hardware) breakout box and a DOS based breakout-box program how my Latitude C840 ports behave. It is of great importance, which OS initializes the ports, since that's, where the control resides...
If you are interested, e-mail me at "petrolf(at)t-online.de", I'll can supply the breakout-box program as an attachment to the reply.
flortep
xcable
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July 16th, 2004 12:00
heath holcomb