ReceiveByte

Interface

VAR_OUTPUT
    ByteReceived: BOOL;
    ReceivedByte: BYTE;
    Error: ComError_t;
END_VAR
VAR_IN_OUT
    RxBuffer : ComBuffer;
END_VAR

Description

The ReceiveByte block receives a single character from the interface corresponding to the input variable RxBuffer. If ByteReceived=TRUE after the call, then the data byte received is available in the output variable ReceivedByte. Otherwise no data has been received.

Note

Whenever a the ReceiveByte block is processed in a PLC task that is running slower than the communication with the hardware, it must be remembered that more than one character can be made available in each PLC cycle. The characters received should therefore be read out within a loop:

REPEAT
    Receive(RXbuffer:=RXbuffer);
    IF Receive.ByteReceived THEN
    (* evaluate character*)
    END_IF
UNTIL NOT Receive.ByteReceived
END_REPEAT

The number of passes through the loop is inevitably limited by the size of the receive data buffer (presently 300 bytes), so that an endless loop need not be feared.