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[Reply #15 on:]

i read this i even used communication example of RS command in this project

Care to share?

Are you saying that the example only showed sending a '3'? Hard to believe but possible.

As for the handshaking, I haven't dealt with that for 20-odd years and I can't remember what does what these days. You could probably get away with tying a couple of lines to active levels or together, the signals in question are CD, DTR and DSR.

But without the access to the proper protocol spec I see little point in carrying on.

______
Rob

[Reply #16 on:]

  Hi,
  I also had this problem that Arduino serial is not read by some devices because it is not "real" rs232. 
  I had to get a component that would clean up the arduino serial, like this $2.50 component on ebay:
http://www.ebay.com/itm/RS232-TTL-Converter-Module-Serial-Board-MAX232CSE-Transfer-Chip-atmega16-/181006995656?pt=LH_DefaultDomain_0&hash=item2a24db90c8
Paul

[Reply #17 on:]

Hi Paul ,
do you mean by not "real" rs232 the signal voltage level ? cos i checked with the PLC manufacturer and its signal is 0-5V DC
or is it a protocol matter as Rob mentioned ?
can you tell me the devices you tried to connect with

[Reply #18 on:]

To connect to a pc or one of our devices via db9 connector I needed this device to create true TTL serial. 

http://en.wikipedia.org/wiki/Transistor%E2%80%93transistor_logic