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modbus_RS485

Created by: Out Control at: 7/27/2014 6:49 PM (8 Replies)

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7/27/2014 6:49 PM	Rate (0)
Out Control Posts: 204 Rating: (1)	Dear all, I use PLC s7-1200 CPU 1214C and RS485 module for communicate with other device by RS485 i built my program as shown in attached file but i face a problem an error 80C8 also i note that whn i download program must be the module configured direct through MB_COMM_LOAD with out configured it in device configuratin but thats didn't hapen .. please any help if my program worng ..or how to communicate with my device Regards Attachment modbus_trial.zip (159 Downloads)
Out Control Posts: 204 Rating: (1)
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7/27/2014 7:37 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 3/17/2025 Posts: 15724 Rating: (2487)	Out Control Dear all, I use PLC s7-1200 CPU 1214C and RS485 module for communicate with other device by RS485 i built my program as shown in attached file but i face a problem an error 80C8 also i note that whn i download program must be the module configured direct through MB_COMM_LOAD with out configured it in device configuratin but thats didn't hapen .. please any help if my program worng ..or how to communicate with my device Regards The biggest issue for reliable rs485 communications for the s7-1200 is the establish the proper starting and stopping conditions for a successful message send/receive. The message start and stop configuration have many "or" conditions. Selecting the right combination for your baud rate is essential for success. I had to do a lot of work with Siemens early on to figure this out. Basically I ended up doing a capture session to see the inbound message content, and measured the details to get the intermessage time-out setting right. If you are getting successful receipt, that's great. If you are getting successful outbound messages received in your field devices, that's even better. What is working and what is not working?
	science guy
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7/28/2014 9:31 AM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 3/16/2025 Posts: 223 Rating: (1)	hi, For referance please look at the following link , i have face such situation somehow it has solved. */tf/WW/en/Posts/111498#top*

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7/31/2014 2:06 PM	Rate (0)
Out Control Posts: 204 Rating: (1)	Dear, i try to set parameters of time out and baudrate but no new result , same i have error status 80C8 slave time out , please check my program if any error in it Regards
Out Control Posts: 204 Rating: (1)
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7/31/2014 2:51 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 3/17/2025 Posts: 15724 Rating: (2487)	Out Control Dear, i try to set parameters of time out and baudrate but no new result , same i have error status 80C8 slave time out , please check my program if any error in it Regards Ok, here's a few suggestions, though not 100% accurate or tested. 1. Take a look at the Help documentation for MB_MASTER. In the help tree to the left shows the Sample Program for Modbus Master. Look at that. 2. MB_MASTER for read: a. P#DB3.DBX6.0 WORD n .. where n is max message size in WORDS you are going to handle b. if that does not fix the read, change DATA_ADDR to 50079 rather than 450079. 3. MB_MASTER for send: a. P#DB3.DBX2.0WORD 2... assuming you are sending 2 words c. if that does not fix the write, change DATA_ADDR to 5 rather than 400005
	science guy
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7/31/2014 8:34 PM	Rate (0)
Out Control Posts: 204 Rating: (1)	Dear many thanks for your response, dear i try to use PC as a slave for PLC then i can monitoring all adresses i typed in PC and also i use PC as master for my communicated module and also working without any problem but when i connected PLC with my communicated module i face this problem , MB_master still busy without any reading also didn't give me any feedback error or done or reciving adresses i think there are some settings in end/start message but really i didn't understand how can i manage Please help mee .... i think i'm to much near to find solution Regards
Out Control Posts: 204 Rating: (1)
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7/31/2014 9:21 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 3/17/2025 Posts: 15724 Rating: (2487)	Can you do a screen shot of the comm load block status to make sure is it successful at initializing the rs485 port? Also, a screenshot of the blocks you are using to send / receive and the captured status when it returns an error would be really helpful. And lastly, back to the original points made earlier, please verify against the rs485 module documentation for 2-wire communication that the wiring is proper. If you have a protocol analyzer or o-scope, or scopemeter, please verify the signals are being sent out of the module. If the TX LED is not blinking, no packet is being sent. If the RX LED is not blinking, no packet is detected. This could be adjusted with the message receive configuration options. If the last character in every valid MB message is known, you could say, end with a specific character followed by some amount of time. That time needs to be calculated so it is proper for your Modbus message. If something is sending on the network very fast, 2 sec timeout is very long and may never be satisfied.
	science guy
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This contribution was helpful to 1 thankful Users Out Control

8/1/2014 12:54 PM	Rate (0)
Out Control Posts: 204 Rating: (1)	Dear, Thanks for your support...now our communication is working with the same software ..that's meanning initialization is ok and MB_MASTER is ok we check connection and we adjust recieve message start and stop for limited length and starting character and it's working but when we adjust recieve message as default again it's also working Really till now i didn't understand whts happen and where is the problem Regards
Out Control Posts: 204 Rating: (1)
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This contribution was helpful to 1 thankful Users 0_Einstein

8/1/2014 1:25 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 3/17/2025 Posts: 15724 Rating: (2487)	Out Control Dear, Thanks for your support...now our communication is working with the same software ..that's meanning initialization is ok and MB_MASTER is ok we check connection and we adjust recieve message start and stop for limited length and starting character and it's working but when we adjust recieve message as default again it's also working Really till now i didn't understand whts happen and where is the problem Regards I am glad my first post's first sentence actually applies to your solution. More importantly, you have it working. And as a by-product, I learned you do not necessarily need to be so specific in following the sample examples to get things to work
	science guy
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This contribution was helpful to 1 thankful Users Out Control

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