There is a message system which does not appear to be document in the OI spec. This appears to be a a canonical terminal type serial interface in which messages come back such as firmware version and stuff. I am not sure how to determine what the end of this type of message is? It is a fixed number of end lines? or Bytes. One message seems to indicate STR730 which would be a 730 byte string.
The open interface spec seems to indicate a non canonical interface spec in which you read a fixed number of bytes with no processing of end lines. Is this correct?