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7.5 General-purpose Serial Communication
7.5.1 Overview
- In general-purpose serial communication, data is sent and received over the communication port 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 communication port by means of
an FP0R program and the FP0R 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 PLC 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 communication port.
Receiving data
Data received from the communication 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.
- 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.
- 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 4094 bytes.
Key Point: In the compatibility mode with the FP0 (FP0 compatibility mode),
the F159(MTRN) instruction is changed to the F144(TRNS) instruction.
Communication Port
Tool port
COM port
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