Hello,

I have the same problem. I'm using: ET200 CM Ptp 6ES7137-6AA01-0BA0.

There is no Hardware Address in that area. No %I4.0, no %IB4, no %IW4, no %ID4 up to address 50, while the CM Ptp uses only a few bytes

I moved all my addresses above 50, and yet the PLC gives this error. The only way it seems to go away is by making the CM Ptp put it's data starting from address 4 or by changing the hardware module to 6ES7137-6AA00-0BA0 (only in the project).

But neither of this solves the actual problem: Modbus over RS485 on 2 wires does not work. Led on TX blinks but no actual data is transmitted over it. (our team looked it up over osciloscope).

Modbus RTU blocks are V3. Later versions are not compatible for some reason. Version 2 gives the same result.

Modbus Master gives back response timeout error as if the partner is not responding. (which is legit since no data is transmitted to slave)

We even changed the ET200 PLC and the CM Ptp with new ones. Partner of Modbus was changed as well, but he is fine we checked Modbus RTU (on RS485 2 wire mode) on it with a s7-1200 and works just fine.

Firmware used on ET200 PLC is 2.9, and TIA Portal V17.

All hardware settings of CM Ptp are set as we always used it for 2 wire mode for the Older version of CM Ptp.

Wiring was done on pin 12 and 14, as we always have done for previous modules for 2 wire mode. We also changed wires between pins 12 and 14 with the same result, (sometimes RS485 is manufactured with inverted polarity on the behalf of partner).

For some reason the HW_ID is no longer showing up... in TIA Portal V17. I only found it in the Tags section at constants.

We recently migrated to V17 for this exact problem as according to datasheet ET200 CM Ptp 6ES7137-6AA01-0BA0 is available only from TIA V17 or newer. Maybe I'm missing something.

Any help is much appreciated.

Regards.

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Split from I/O Read access error (I Address 4) in FB 614.

What OB is running when the I/O read access error happens?

If you disable the MB blocks, does the error go away?

If you review the working pane for Devices & Networks from the project tree (above the PLC), and then expand the addressing area while checking each device configured in the hardware, you can see every instance of Inputs.

Now in your logic, if you are using any peek commands, verify they are not reading Input, and if so, that they are not reading address 4.

In your PLC tag table, show all tags.  Sort by address.  Scroll down to the inputs.  Is there anything pointing to address I..4?

A few screenshots would be helpful on that.

As to the MB stuff, how is the hardware configured for the CM PTP module so that it will accept data and send data?  The default values rarely work the way real world applications work - they instead default to a situation where nothing works (if I recall correctly).

For 2-wire mode, you have to create a break in sending so it can receive in your logic.

I have used 2-wire mode, and I really dislike being forced to use it.  I prefer replacing cabling over coding an application to insert pauses between sends and receives.  It's very tricky to do efficiently.

Supposedly the hardware does that for us, but my experience has been that we really need to help it along a bit to get reliable comms.

A screenshot of the send and receive hardware configuration would be appreciated.  If they are set up correctly, data should flow and the comms led(s) should blink as data is sent / received.

Are they (LEDs) blinking all the time, sometimes, only at startup, or never?

ALRD

Hello,

I have the same problem. I'm using: ET200 CM Ptp 6ES7137-6AA01-0BA0.

There is no Hardware Address in that area. No %I4.0, no %IB4, no %IW4, no %ID4 up to address 50, while the CM Ptp uses only a few bytes

I moved all my addresses above 50, and yet the PLC gives this error. The only way it seems to go away is by making the CM Ptp put it's data starting from address 4 or by changing the hardware module to 6ES7137-6AA00-0BA0 (only in the project).

But neither of this solves the actual problem: Modbus over RS485 on 2 wires does not work. Led on TX blinks but no actual data is transmitted over it. (our team looked it up over osciloscope).

Modbus RTU blocks are V3. Later versions are not compatible for some reason. Version 2 gives the same result.

Modbus Master gives back response timeout error as if the partner is not responding. (which is legit since no data is transmitted to slave)

We even changed the ET200 PLC and the CM Ptp with new ones. Partner of Modbus was changed as well, but he is fine we checked Modbus RTU (on RS485 2 wire mode) on it with a s7-1200 and works just fine.

Firmware used on ET200 PLC is 2.9, and TIA Portal V17.

All hardware settings of CM Ptp are set as we always used it for 2 wire mode for the Older version of CM Ptp.

Wiring was done on pin 12 and 14, as we always have done for previous modules for 2 wire mode. We also changed wires between pins 12 and 14 with the same result, (sometimes RS485 is manufactured with inverted polarity on the behalf of partner).

For some reason the HW_ID is no longer showing up... in TIA Portal V17. I only found it in the Tags section at constants.

We recently migrated to V17 for this exact problem as according to datasheet ET200 CM Ptp 6ES7137-6AA01-0BA0 is available only from TIA V17 or newer. Maybe I'm missing something.

Any help is much appreciated.

Regards.

I solved my problem.

It turns out that the I/O Read access error was unrelated to Modbus RS485 i was using. I had a MODBUS TCP that that had active code that I did not use anymore and forgot about it. Here was a Receive_P2P block in this Modbus TCP block that did not show up in cross reference. The port (HW_ID) that was set there was non-existent in the actual configuration. Once I removed that code, the error disappeared.

Modbus comm load also had a parameter "Mode" that for some reason got reset from 4 to 0, maybe while changing the version of Modbus blocks, since the DB was created again.

Somehow the developer of this block decided that Baud rate, Parity, Resopnse_to and so on... is more important than this "Mode" parameter as it was not an input in the block but rather a Static variable. Also for some reason setting the operating mode to RS485 2 wire mode in the hardware configuration is not enough.

Thank you for your quick reply.

I solved my problem.

It turns out that the I/O Read access error was unrelated to Modbus RS485 i was using. I had a MODBUS TCP that that had active code that I did not use anymore and forgot about it. Here was a Receive_P2P block in this Modbus TCP block that did not show up in cross reference. The port (HW_ID) that was set there was non-existent in the actual configuration. Once I removed that code, the error disappeared.

Modbus comm load also had a parameter"Mode"that for some reason gotreset from 4 to 0, maybe while changing the version of Modbus blocks, since the DB was created again.

Somehow the developer of this block decided that Baud rate, Parity, Resopnse_to and so on... is more important than this"Mode"parameter as it was not an input in the block but rather a Static variable. Also for some reason setting the operating mode to RS485 2 wire mode in the hardware configuration is not enough.