comms check 1

[richerdick]

i am trying to monitor activity from a comms port on a plc with some software i have downloaded. The plc comms port is rs485 the pc is rs232. Can i just use the txd+ rxd+ to the tx rx of the PC i am not looking to analyse any data just to see that it is being transmitted.

 

[itsmoked]

Nope one is differential the other is not.

There are scads of converters out there.

Look at BlackBox.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

Richerdick,
You can use a PC with RS-232 port to monitor RS-422 & 485. I find this very helpful when dealing with unknown equipment.
Connect the RXd of the PC to the Sig- line of the 422/485 and ground.
A couple of tips:
If you are not sure which pin of RS-232 is RXd measure with a multimeter to signal ground TXd will have voltage on it RXd will not.
When you are trying to get communications for the first time run at a slow baud rate e.g. 1200 until you are able to get the parity and stop bits of the two devices to match.

It's also possible to get one differential signal device to respond to RS-232 TXd by connecting the 232 RXd & TXd together (loopback) and to the Sig- line with the Sig+ line connected to RS-232 Signal ground. A word of caution though, the 232 port signal level may be too high for the differential device so measure first and drop it with a voltage divider if required.
Regards
Roy

 

[itsmoked]

That's interesting Roy. A little desperate.. But interesting.

I would still use one of these unless I was in the great outback or Antarctica.

http://www.accesio.com/go.cgi?p=../serial/conv232.html

http://www.bb-elec.com/product_family.asp?FamilyId=15&TrailType=Sub&Trail=12

http://www.l-com.com/item.aspx?id=9165

http://www.lowcostconverters.com/Converter.htm

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

Keith,
I quite agree, for a permanent solution, but for testing it works fine. You can't always wait a week for parts to arrive.
Regards
Roy

 

[mikek10]

You can get USB to serial converters (232/422/485) from easysync, they usually deliver next day. Programing-wise they are just like a standard comm port