I ran into a similar situation with an S7-1200 using RS485 comms.  It was old hardware / firmware that allowed a startup timing glitch to have the same problem you described.

The solution we came up with (after contacting Siemens Support) was to power up the RS485 through a PLC digital output (we had relay outputs, otherwise, we would have used an external relay).

At PLC startup, we turn on a digital output.

That forces the PLC to always be running once the RS485 module powers up and becomes available.

I do NOT recommend this approach because it generates PLC diag buffer entries EVERY time the PLC stops and starts.  It generates a system "fault" which will halt the PLC - unless a diagnostics error interrupt OB exists in the PLC/project.  Once you put that OB in, you become responsible for handling the various diag errors than can happen at runtime and then decide whether to issue a PLC stop, or do something else.

Please post .zip archive containing:

• screenshot your RS485 comms call(s)
• screenshot of the hardware config for the module/port
• screenshot of any runtime configuration block calls

555aleksandr777

Hello! I am currently working on a project with several devices connected via RS485 freeport to the CM PTP 6ES7 137-6AA01-0BA0 module. The problem is that when power is supplied to the PLC, the exchange does not occur. Only after removing the module "hot" and then installing it in place, the exchange begins.

Devices of our development with the RS485 module. The type of device does not affect the behavior of the system - when connecting a PLC to a PC (via an RS485-USB adapter, Terminal1_9_b is running on the PC) the situation is the same.

Has anyone encountered a similar problem? What could be the solution?

Going to reply with things I see quickly in hopes they actually solve the real problem.

In 2.jpg & 3.jpg, the port # is 260.  Instead of 260, find the System Constants in the PLC tag table, and "float" it so you can drag the module's system constant.

This way, if Portal decides to change the constant's value, the next compile and hardware download automatically fixes it.

What output values do you get in the watch table for the tags in 2.jpg?  Do you use the NDR output to increment a tag - so you can see a count of the number of successful messages received?

I see you capture the error / status.  What values are you seeing?  Same for outputs for sending on 3.jpg?

In my experience using PTP modules, the hardware configuration for sending and receiving messages, and defining what they look like - to help the module discriminate starting and ending on PTP message data start could be "always starts with bytes 16#00 16#01 16#FF.  Ending message configuration could be 16#00, or 16#0D 16#0A, or 16#FF, or no new bytes within 10 ms.

Your remote device(s) tell you what that will look like.

I find setting the start message is usually easy - look for data after x ms of nothing.  However, finding the optimal end message configuration is tricky and will likely gain you the most with the least amount of PLC code change.

I suggest adjusting the PLC logic so you can drive the RS485 send / receive from a watch table where you use a watch table tag on a -|p|- into the send REQ input.  That way, you get ONE send for each "lightning bolt" modify value click in the watch table, and that means the saved error, or incremented tag counting Done true pulses (successful send) for each send attempt.

Then you can find / fix whatever error is provided.

For receiving, that's strictly hardware configuration with the start/stop message detection settings.

Remember to change those while offline, and download the hardware config changes so they take affect right away.

555aleksandr777

That is, after switching on, the connection is not established. After removing and then installing the CM PTP unit, the connection appears. If you turn off the PLC and then turn on the power, then the connection disappears again. Also, the connection disappears when switching the PLC to stop and then to RUN. Additional initialization of PORT_CONFIG does not help to solve the problem.

Thank you very much!

I tried early to put HW ID of input PORT - it is not essential. 

Now I put HW ID again - you can see screenshots online. It not solved a problem - only after removing and inserting the block does the system start working correctly. And the data exchange works correctly until you switch the PLC to stop, or turn off and turn on the PLC power. 

Yes, I use STX and ETX for mark start and stop frame. The problem is not in the content of the messages, but in the initialization of the CM PTP module.

I want to try to connect the CM PPTP module via an ET station. First, start the PLC, then supply power to the ET station.

0_Einstein

I see you capture the error / status.  What values are you seeing?  Same for outputs for sending on 3.jpg? 

I don't have any errors - 

SEND_P2P - NDR is ON, when I send, ERR - 0

Receive_P2P - not receive - ERR - 0