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Error 8070 on Modbus RTU connection to 15 Slaves

Created by: Sami2040 at: 3/24/2025 7:12 AM (6 Replies)

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3/24/2025 7:12 AM	Rate (0)
Sami2040 Advanced Member Joined: 4/10/2018 Last visit: 7/24/2025 Posts: 47 Rating: (1)	Hello Gents, Pls. I need your support for the below project: My application is to read data from 15 energy meters via Modbus RTU with CPU S7 1214 DC/DC/DC and CB1241, the problem is up to 7 devices the program runs perfectly and able to read data from meters, but after adding extra meters to the program, there is no any data transfer between CB and Modbus network and getting Status Error 8070 on all MB_Master blocks, meaning of this message is that all internal instance memories are in use, I tried to separate the EN input for each MB_Master blocks to not be active at same times but still facing 8070 error on all blocks, pls. need your kind support to solve my problem. your contribution will be highly appreciated!

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3/24/2025 7:36 AM	Rate (0)
gvatte Advanced Member Joined: 1/24/2021 Last visit: 8/29/2025 Posts: 118 Rating: (15)	Hello Sami, Im not sure, but it might have something to do with the amout of connections your plc can have. See user manual Link under chapter "12.4 Asynchronous communication connections" Sami2040 Hello Gents, Pls. I need your support for the below project: My application is to read data from 15 energy meters via Modbus RTU with CPU S7 1214 DC/DC/DC and CB1241, the problem is up to 7 devices the program runs perfectly and able to read data from meters, but after adding extra meters to the program, there is no any data transfer between CB and Modbus network and getting Status Error 8070 on all MB_Master blocks, meaning of this message is that all internal instance memories are in use, I tried to separate the EN input for each MB_Master blocks to not be active at same times but still facing 8070 error on all blocks, pls. need your kind support to solve my problem. your contribution will be highly appreciated! Br
	Please feel free to rate my contribution if it was helpfull :)
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3/24/2025 7:57 AM	Rate (0)
Sami2040 Advanced Member Joined: 4/10/2018 Last visit: 7/24/2025 Posts: 47 Rating: (1)	Thanks Mr. gvatte for your kind reply, as per the manual chapter 12.4 is for Universal serial interface (USS) communication, my application with Modbus RTU and I guess up to 31 slaves could be configured for each Master.

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3/24/2025 2:15 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/9/2025 Posts: 16079 Rating: (2514)	For MB RTU, you only need one connection. You simply have to rotate the settings each time you attempt to remotely read. If you read the same data from all 15 meters, you only need to change the MB address and redirect the returned output before rotating to the next meter. You do also need to handle errors correctly. You should download a sample Siemens application using MB/RTU and a CB1241 to see how Siemens rotates the in/out parameters and handles errors and see what you are missing. Sami2040 Hello Gents, Pls. I need your support for the below project: My application is to read data from 15 energy meters via Modbus RTU with CPU S7 1214 DC/DC/DC and CB1241, the problem is up to 7 devices the program runs perfectly and able to read data from meters, but after adding extra meters to the program, there is no any data transfer between CB and Modbus network and getting Status Error 8070 on all MB_Master blocks, meaning of this message is that all internal instance memories are in use, I tried to separate the EN input for each MB_Master blocks to not be active at same times but still facing 8070 error on all blocks, pls. need your kind support to solve my problem. your contribution will be highly appreciated!
	science guy
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3/25/2025 8:07 AM	Rate (0)
Sami2040 Advanced Member Joined: 4/10/2018 Last visit: 7/24/2025 Posts: 47 Rating: (1)	Thanks Mr. 0_Einstein for your kind support! Here is the problem, I need to read data from 2 different addresses area for each device (72 instantaneous values starting from address 30001, and 22 energy Values starting from address 40095) and that makes my code little bit complected, so for each device I am calling 2 MB_MASTER blocks to handle 2 different reading for each device, and totally I have 30 blocks in my program, as I mentioned, up to 7 devices it worked perfectly but after adding an extra device I faced 8070 error. Now, could you pls. support if possible to have only 2 MB_MASTER blocks for all 15 meters and rotate the address as you mentioned, or I have to separate the block for each memory areas

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3/26/2025 3:36 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 9/9/2025 Posts: 16079 Rating: (2514)	You only need 1 MB_MASTER block for all 15 meters reading each meter with 2 different address groups each read. There will be 30 different sets of MB_MASTER call parameters. I recommend having a single FB to call 30 times. Inside that single FB is the single MB_MASTER block. The trick is to have a sequencer call that FB 30 times with different parameters. The trick is to properly handle every error state, leave the current FB running / enabled until Done or Error output occurs. On Error outputs, you need to properly handle / track them for a given meter. On PLC restart, you need to actively kill any existing connection if you want the very first call to succeed. On power cycle restart, you do not need to do anything with existing connections. However, attempting to disconnect a connection that does not exist simply results in an error stating no such connection exists and you have what you want. Hence, disconnecting a connection at startup is advised, whether any connection exists or not. Try getting a single meter working with this approach, passing in the 3xxxxx parameters first. Once that works, pass in the 4xxxx parameters. Once it completely works for a single meter, add a 2nd meter. The only thing that should change is the address passed to the called FB. So, you should essentially clone the 2 calls for the 1st meter into another FB, and then call that FB 15 times with different MB address each call. Make sense? Build it in pieces and it kind of naturally flows into a set of FBs that manages it all for you. Sami2040 Thanks Mr. 0_Einstein for your kind support! Here is the problem, I need to read data from 2 different addresses area for each device (72 instantaneous values starting from address 30001, and 22 energy Values starting from address 40095) and that makes my code little bit complected, so for each device I am calling 2 MB_MASTER blocks to handle 2 different reading for each device, and totally I have 30 blocks in my program, as I mentioned, up to 7 devices it worked perfectly but after adding an extra device I faced 8070 error. Now, could you pls. support if possible to have only 2 MB_MASTER blocks for all 15 meters and rotate the address as you mentioned, or I have to separate the block for each memory areas
	science guy
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6/12/2025 12:44 PM	Rate (0)
msgsadek Bronze Member Joined: 8/12/2016 Last visit: 9/5/2025 Posts: 108 Rating: (3)	0_Einstein For MB RTU, you only need one connection. You simply have to rotate the settings each time you attempt to remotely read. If you read the same data from all 15 meters, you only need to change the MB address and redirect the returned output before rotating to the next meter. You do also need to handle errors correctly. You should download a sample Siemens application using MB/RTU and a CB1241 to see how Siemens rotates the in/out parameters and handles errors and see what you are missing. Sami2040 Hello Gents, Pls. I need your support for the below project: My application is to read data from 15 energy meters via Modbus RTU with CPU S7 1214 DC/DC/DC and CB1241, the problem is up to 7 devices the program runs perfectly and able to read data from meters, but after adding extra meters to the program, there is no any data transfer between CB and Modbus network and getting Status Error 8070 on all MB_Master blocks, meaning of this message is that all internal instance memories are in use, I tried to separate the EN input for each MB_Master blocks to not be active at same times but still facing 8070 error on all blocks, pls. need your kind support to solve my problem. your contribution will be highly appreciated! Can you send the link of the example you are referring to?

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