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Connecting a device to "CM 1241 (RS422/485)"

Created by: Hakan Tugay at: 11/4/2014 1:01 PM (5 Replies)

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6 Entries

11/4/2014 1:01 PM	Rate (0)
Hakan Tugay Posts: 15 Rating: (0)	Hello all, I have a "CM 1241 (RS232)" and a "CM 1241 (RS422/485)" module connected to S7-1200 CPU. The CM 1241 (RS422/485) module operates in "Half duplex(RS485) two wire operation" mode. I connect a load cell device which has a RS232 interface to the CM 1241 (RS232) module. I use default port configuration options (Baud rate, parity, ...). Using the RCV_PTP function I can read data from the load cell. I connect the same load cell to the "CM 1241 (RS422/485) module over a RS232/RS485 converter. But I cannot read any data using the RCV_PTP function. Shall I use a different function for the CM 1241 (RS422/485) module? The RS232/RS485 converter I use is a very simple device. Is it possible that this converter is inappropriate for the CM 1241 module? Regards, Dert
Hakan Tugay Posts: 15 Rating: (0)	Last edited by: Dert at: 11/4/2014 1:02 PM
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11/5/2014 12:07 PM	Rate (1)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 3/10/2025 Posts: 1557 Rating: (540)	I expect that there is an issue with the convertor. These convertors can work in one of 2 ways:- 1) They snoop the RS232 TXD line and enable their transmitters on the RS485 side when they see the start of a transmission (start bit), and disable their transmitters on the RS485 side when thet see the end of a transmission (stop bit). 2) They use an external signal to say when to enable the transmitters on the RS485 side. The RTS line is normally used for this purpose. So you will have to setup the parameterisation such that RTS is set high before the transmission starts and dropped low again after the transmission has ended. This can be achived by using the "Automatic use of the RS232C signals" option and selecting appropriate values for the "Time to RTS off" and "Data Output Waiting Time" settings. See the online help for more details. Also some convertors are port powered and need power from the RS232 side to power the electronics. They usually get this from CTS / DSR lines, which will need to be in their active state so that they can provide power to the convertor. I cannot say much more until I know what convertor you are using.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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11/17/2014 3:40 PM	Rate (0)
Hakan Tugay Posts: 15 Rating: (0)	This issue is solved, I just found out what the problem is. I connected the load cell to a "CM 1241 (RS232)" module with a straight serial cable and it worked just fine. While trying it with the "CM 1241 (RS422/485)" module over a RS232/RS485 converter I used also two straight cables. One from the load cell to the converter, second from the converter to the "CM 1241 (RS422/485)" module. I just changed both straight cables to cross cables and now I can read data from the load cell.
Hakan Tugay Posts: 15 Rating: (0)
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This contribution was helpful to 2 thankful Users smiffy Min_Moderator

3/30/2015 11:56 AM	Rate (0)
haducnha Posts: 5 Rating: (0)	Hakan Tugay This issue is solved, I just found out what the problem is. I connected the load cell to a "CM 1241 (RS232)" module with a straight serial cable and it worked just fine. While trying it with the "CM 1241 (RS422/485)" module over a RS232/RS485 converter I used also two straight cables. One from the load cell to the converter, second from the converter to the "CM 1241 (RS422/485)" module. I just changed both straight cables to cross cables and now I can read data from the load cell. Hello everyone ! I m having the same problem. Can you show me the diagram RS232 to RS232/485 convert to RS485 ? thank you
haducnha Posts: 5 Rating: (0)
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4/3/2015 9:56 AM	Rate (0)
MS1981 Silver Member Joined: 4/14/2010 Last visit: 2/8/2025 Posts: 525 Rating: (11)	Dear Smiffy, Please see attached, only Tx flashing nothing to receive we have CM 1241 module with V1.0 The message appear 8200 Port is busy processing a transmit request. Thanks. Attachment Desktop.zip (576 Downloads)
	MS
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3/16/2017 10:45 AM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4766 Rating: (122)	New question published by Chaya Naga Sumanth is split to a separate thread with the subject CM-1241, not able to write data. Best regards Min_Moderator

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