piclist 2002\10\03\172736a >
Thread: how to check rs232 DTR pin.
face BY : Wagner Lipnharski email (remove spam text)

andre abelian wrote:
> Hi to all,
> I have a software it suppose to turn on
> Rs232 dtr line on and off I think it
> Doesn't work. What I remember on DB9 pin 4
> Is DTR but what I do not know is DTR open drain?
> Just incase I added 10k pull up resister. I still
> Do not see any changes. I already checked RX and TX
> On same com port they work fine. My question is how
> Can I check RS232 DTR line on and off?
> Any help will appreciate.
> Andre
> --
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What side of the interface is your device?
DTE (equipment) or DCE (modem) ?

If you are trying to control DTR, I understand you should be the DTE
(Equipment), since DTR means "Data Terminal Ready", a circuit that tells
the MODEM that the "terminal" is ready.   If this is true, then your
circuit should drive the DTR via a RS232 chip, or if you can, control DTR
with +8 and -8V (from 6 to 14V is ok), with transistors, proper RS232
drivers or something like that.

DTR or any other RS232 circuit is open drain, all of them are drivers for
positive and negative voltages.

Why don't you explain better your installation, pinouts, circuits, levels,
then probably we could help better.

This is the pinout of the DC9 connector:

DC-9 Connector
Pin   Signal             | Pin  Signal
1  CD   Carrier Detect   | 6  DSR  Data Set Ready
2  RXD  Receive Data     | 7  RTS  Request to Send
3  TXD  Transmit Data    | 8  CTS  Clear to Send
4  DTR  Data Term. Ready | 9  RI   Ring Indicator
5  GND  Signal GND       |

Wagner Lipnharski - UST Research Inc
Orlando FLorida - USA - http://www.ustr.net
/_/_/_/ Atmel AVR Consultant /_/_/_/

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See also: www.piclist.com/techref/io/serials.htm?key=rs232
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