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7 Serial Communications
NX-series Communications Interface Units User’s Manual (W540)
7-2 How Data Is Sent and Received
7
7-2-2 How Data Is Received
When data is received, the receive data is first stored in the receive buffer in the CIF Unit, as shown in
the following figure, before the data is sent to the CPU Unit or communications master. The receive buf-
fer size is 5,120 bytes per port.
The following procedure is used to receive data.
1 The receive data on the serial line is stored in the receive buffer in the CIF Unit.
2 In each I/O refresh cycle, the receive data in the receive buffer in the CIF Unit is sent in order to
the CPU Unit or communications master.
The size of receive data that is transferred each time depen
ds on the divided data size setting.
You can change the divided data size to between 4 and 80 bytes. The default setting is 20
bytes.
Precautions for Correct Use
The CIF Unit may not store receive data that is on the serial line in the receive buffer when the
Controller power supply is turned ON or during initialization processing immediately after the
CIF Unit is restarted. A parity or framing error may occur.
7-2-2 How Data Is Received
Send buffer
Serial communi-
cations device
CPU Unit or
communications
master
CIF Unit
NX bus or
communica-
tions cable
Serial line
Receive buffer
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