7.4 Communication Function 2: General-purpose Serial
Communication
7.4.1 General-purpose Serial Communication
Overview
• In general-purpose serial communication, data is sent and received over the COM ports to and from an
external device such as an image processing device or a bar code reader.
• Data is read from and written to an external device connected to the COM port by means of an FP-X
program and the FP-X data registers.
Outline of operation
To send data to and receive it from an external device using the general-purpose serial communication
function, the data transmission and data reception functions described below are used. The F159
(MTRN) instruction and the “reception done” flag are used in these operations, to transfer data between
the FPΣ and an external device.
Sending data
Data to be transmitted from the PLC is stored in the data register used as the send buffer (DT). When
F159 (MTRN) is executed, the data is output from the COM port.
• The terminator specified in the system
register is automatically added to the data
that has been sent.
• The maximum volume of data that can be
sent is 2048 bytes.
Receiving data
Data received from the COM port is stored in the receive buffer specified in the system register, and the
“reception done” flag goes on. Data can be received whenever the “reception done” flag is off.
• When data is being received, the “reception
done” flag is controlled by the F159 (MTRN)
instruction.
• No terminator is included in the stored data.
• The maximum volume of data that can be
received is 4096 bytes.
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