How to use FB64 T_RECV to receive variable-length messages?

I am trying to use FB64 T_RECV to read variable-length messages from a host PC application.
Each message is terminated with a control character, normally <LF> but can be changed.
My proposed solution is to keep EN_R true and LEN set to 1 and monitor the received data until the expected control character is received, then set EN_R false. Is this the correct way to do it, or is there a better way?
Presumably, one character will still be expected after EN_R has been negated, so BUSY will remain true until that character appears.

Does the NDR output go true and the BUSY output go false each time LEN characters are received, even when EN_R is still true?

PS I am using the IM151-8PN/DP integral ethernet ports for this communication.

I admit the way you mentioned, to poll each single byte would work too. As you have a message end signal you will surely be successful to run it this way. But it will take a while especially if you have longer frames to receive.

Let me try to answer some of your questions too. The NDR on the TRCV will be high each time the FBreceives a Byte and posts this to the Buffer you provide. As long as the NDR is high, the Busy is low.

As an alternative to your mentioned procedure I would recommend the use of a Pre-Header in each telegram. The information there may only contain the length of the Telegram send. With this information you may call the TRCV only once and the system may be much faster than with the procedure you mentioned.

I hope I could give you some idea.

Best regards