Read ascii with CP340

[jtk]

Hello, I need to read ascii serial data rs485 with a CP340. I have not started yet, but I like to be prepared. Say the data block is 300 bytes in total and the block begins with the word "start". As far as I understand, the P_RCV block is used to read data from CP340. It feels like I have to tell this block that the data block starts with the word "start" and the actual data begins after these bytes. Where and how is this done? The system is a S7-300. Regards jtk