Panasonic FP2 Series, User Manual

Page: 69 / 102

Precautions Regarding Serial Data Unit Operation and Programs
FP2 Serial Data Unit
5 − 5
5.2 Precautions Concerning Communication
When sending data
If the system is operating with a valid start code, be aware that the data from the most
recent start code to the end code will be sent as one frame.
STX STX ETX
STX: Start code
ETX: End code
When start code is valid: 1 frame
When start code is not valid
When the start code is valid, data sent without a start code will cause an error and cannot
be sent.
When the start code is valid, any other code existing before the start code will cause an
error, and the data cannot be sent.
The data being sent should always be written so that it begins with a start code.
For sample time out and retry programs, refer to section 8.1.2.
5.2.2 End Codes for Communication
When sending data:
If there is no end code in the data being sent, a “Sent message length error” will occur,
and it will not be possible to send data from the serial data unit.
When receiving data:
If data is received without an end code, the received data will not be stored into the
received buffer of the shared memory, so before sending data from the RS232C device
on the other side, be sure an end code has been specified.
5.2.3 Operation If a Communication Error Occurs
If a communication error occurs, the ERR LED on the operation status display of the
serial data unit lights, but this LED goes out automatically when normal data is received.