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read slave by mb_master

Created by: saleh at: 12/16/2014 2:08 PM (12 Replies)

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12/16/2014 2:08 PM	Rate (0)
saleh Posts: 124 Rating: (4)	I want to read value of sensor (slave) by 1214c cpu (master). I recieved this response when sensor connected to Modbus poll software (as master): Tx:02 03 00 00 00 01 C4 38 Rx:02 03 02 00 13 38 F6 the value of sensor is 13 (in Rx). MB_master is always busy and I don't know. MB_ADDR is slave address? ADD_PTR is word type, it's correct? Attachment mb master.jpg (420 Downloads)
saleh Posts: 124 Rating: (4)
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12/16/2014 3:56 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/16/2025 Posts: 16106 Rating: (2515)	saleh I want to read value of sensor (slave) by 1214c cpu (master). I recieved this response when sensor connected to Modbus poll software (as master): Tx:02 03 00 00 00 01 C4 38 Rx:02 03 02 00 13 38 F6 the value of sensor is 13 (in Rx). MB_master is always busy and I don't know. MB_ADDR is slave address? ADD_PTR is word type, it's correct? It is not supposed to matter, but it seems it sometimes does. Try this: DATA_PTR change from "Data_block_1" to "DB3.DBX0.0 BYTE 2" Capture the status output to a tag and save it every time either DONE/BUSY/ERROR come true so you can track what the status value is telling you. Is this of any use?
	science guy
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12/16/2014 7:32 PM	Rate (0)
saleh Posts: 124 Rating: (4)	huggy_d1 saleh I want to read value of sensor (slave) by 1214c cpu (master). I recieved this response when sensor connected to Modbus poll software (as master): Tx:02 03 00 00 00 01 C4 38 Rx:02 03 02 00 13 38 F6 the value of sensor is 13 (in Rx). MB_master is always busy and I don't know. MB_ADDR is slave address? ADD_PTR is word type, it's correct? It is not supposed to matter, but it seems it sometimes does. Try this: DATA_PTR change from "Data_block_1" to "DB3.DBX0.0 BYTE 2" Capture the status output to a tag and save it every time either DONE/BUSY/ERROR come true so you can track what the status value is telling you. Is this of any use? I used "P#DB3.DBX0.0 BYTE 2" and capture DONE/BUSY/ERROR come true. the result in 2 minutes: 1 done 1000 busy 10 error
saleh Posts: 124 Rating: (4)
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12/16/2014 7:37 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/16/2025 Posts: 16106 Rating: (2515)	saleh huggy_d1 saleh I want to read value of sensor (slave) by 1214c cpu (master). I recieved this response when sensor connected to Modbus poll software (as master): Tx:02 03 00 00 00 01 C4 38 Rx:02 03 02 00 13 38 F6 the value of sensor is 13 (in Rx). MB_master is always busy and I don't know. MB_ADDR is slave address? ADD_PTR is word type, it's correct? It is not supposed to matter, but it seems it sometimes does. Try this: DATA_PTR change from "Data_block_1" to "DB3.DBX0.0 BYTE 2" Capture the status output to a tag and save it every time either DONE/BUSY/ERROR come true so you can track what the status value is telling you. Is this of any use? I used "P#DB3.DBX0.0 BYTE 2" and capture DONE/BUSY/ERROR come true. the result in 2 minutes: 1 done 1000 busy 10 error 1 done is great. 10 error and 1000 busy may be you are activating the Modbus read faster than the slave can respond. For testing purposes, wait an entire second between Modbus reads so you as a human can see it happen and watch the counter and status value change. For those errors, what status code were you receiving? The REQ line needs to only be allowed to come back on if you receive a DONE or ERROR result from the read request.
	science guy
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12/16/2014 8:34 PM	Rate (0)
saleh Posts: 124 Rating: (4)	huggy_d1 saleh huggy_d1 saleh I want to read value of sensor (slave) by 1214c cpu (master). I recieved this response when sensor connected to Modbus poll software (as master): Tx:02 03 00 00 00 01 C4 38 Rx:02 03 02 00 13 38 F6 the value of sensor is 13 (in Rx). MB_master is always busy and I don't know. MB_ADDR is slave address? ADD_PTR is word type, it's correct? It is not supposed to matter, but it seems it sometimes does. Try this: DATA_PTR change from "Data_block_1" to "DB3.DBX0.0 BYTE 2" Capture the status output to a tag and save it every time either DONE/BUSY/ERROR come true so you can track what the status value is telling you. Is this of any use? I used "P#DB3.DBX0.0 BYTE 2" and capture DONE/BUSY/ERROR come true. the result in 2 minutes: 1 done 1000 busy 10 error 1 done is great. 10 error and 1000 busy may be you are activating the Modbus read faster than the slave can respond. For testing purposes, wait an entire second between Modbus reads so you as a human can see it happen and watch the counter and status value change. For those errors, what status code were you receiving? The REQ line needs to only be allowed to come back on if you receive a DONE or ERROR result from the read request. status code is 16#0000. I used clock 0.5Hz for set REQ parameter but I got same problem! I used message timeout more (about 1000 ms) but I got same problem! how do I speed down modbus?
saleh Posts: 124 Rating: (4)
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12/17/2014 3:57 PM	Rate (0)
saleh Posts: 124 Rating: (4)	when i use "P#DB3.DBX0.0 BYTE 2" at DATA_PTR, i must have data block that has 1 word data or seperate bytes? because I want to read one holding register.
saleh Posts: 124 Rating: (4)
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12/17/2014 4:24 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/16/2025 Posts: 16106 Rating: (2515)	saleh when i use "P#DB3.DBX0.0 BYTE 2" at DATA_PTR, i must have data block that has 1 word data or seperate bytes? because I want to read one holding register. Take a look at this in F1-Help using search: "Sample program for a Modbus master"
	science guy
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12/17/2014 4:52 PM	Rate (0)
saleh Posts: 124 Rating: (4)	I've read this manual alot of time but Busy still exist!
saleh Posts: 124 Rating: (4)
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12/17/2014 4:56 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/16/2025 Posts: 16106 Rating: (2515)	saleh I've read this manual alot of time but Busy still exist! Is your data block set for compatibility mode (absolute addressing) or symbolic? If you read the F1-help, you would have already set the DB attribute and know the answer. Sometimes it takes someone pointing out the importance of something we read for us to effectively use that information. Perhaps this is the case, perhaps not. Are the Modbus parameters matching what your remote device is expecting?
	science guy
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12/17/2014 5:06 PM	Rate (0)
saleh Posts: 124 Rating: (4)	huggy_d1 Are the Modbus parameters matching what your remote device is expecting? yes those parameters are exactly match and more! i attached images of my work. Attachment image.zip (372 Downloads)
saleh Posts: 124 Rating: (4)
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12/17/2014 5:18 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/16/2025 Posts: 16106 Rating: (2515)	saleh huggy_d1 Are the Modbus parameters matching what your remote device is expecting? yes those parameters are exactly match and more! i attached images of my work. Are you able to do Modbus comms using your PC (laptop) using a test program with the same rs232 communications parameters? baud/parity/stop bits, and so on? It might be a cable issue, communications settings problem, and the best way to test using a known good cable with a laptop and a Modbus test program. If that works, use a cable tester to verify the cables are the same between the PLC cable and the known good cable. If you already did those things, it might be a communications configuration setting on the PLC comm module not working with your Modbus settings.
	science guy
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12/17/2014 5:43 PM	Rate (0)
saleh Posts: 124 Rating: (4)	huggy_d1 Are you able to do Modbus comms using your PC (laptop) using a test program with the same rs232 communications parameters? baud/parity/stop bits, and so on? It might be a cable issue, communications settings problem, and the best way to test using a known good cable with a laptop and a Modbus test program. If that works, use a cable tester to verify the cables are the same between the PLC cable and the known good cable. If you already did those things, it might be a communications configuration setting on the PLC comm module not working with your Modbus settings. I've tested it with test program, and the result of this software to read slave holding register attached as txt file. I've expent a lot of time to do this project, anybody can help me? Attachment rs485.zip (266 Downloads)
saleh Posts: 124 Rating: (4)	Last edited by: saleh at: 12/18/2014 3:18 PM
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12/21/2014 1:42 PM	Rate (0)
saleh Posts: 124 Rating: (4)	Thank you huggy! I used 8N2 and i should use 8E1.
saleh Posts: 124 Rating: (4)
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