Dear experts,

I would like to ask you about freeport communication. So far, I have only used the functions of standard libraries such as Modbus RTU and TCP.

I need to migrate an S7-200 PLC to an S7-1200.

Port 0 of the S7200 is configured in freeport mode. This is used to communicate with an electronic card, manufactured for the application, which receives signals from three position transducers.

The program in the S7200, I attach the program extract, I have managed to understand it, an event 8 of character reception in port 0 is associated with an interrupt (INT_1), where a frame of 14 characters is saved in a memory buffer, when the 14 are counted, the data is saved in a segment of MW memories, a byte with value 1 is sent to the card with the XMT instruction, and the character counter is reset, to then restart the sequence when the next interrupt event occurs.

I created a program on the S7-1200, CPU1214c v4.5, and a CM 1241 module (RS422/485) v2.2. The program is attached. To my surprise, with this simple program and the RCV_PTP function (on network 7), I can read the data, all 14 characters. There are no errors, and the status code is 0. However, with the SEND_PTP function (on network 2), the error bit is 0, and the status codes are 7000 and 7002. I think it's because I don't know how to create the trigger when character 14 arrives.If I don't use the RCV_CFG function, in network 6, I get the same result. 

The values​​of the 14 bytes in the S71200 are the same as in the S7200. But there are moments, a few milliseconds, like a blink, when the values ​​become severely distorted.

------------------------------------------------------------------------------------------
Split from How to program communication using freeport.