Omron CJ - INSTRUCTIONS REFERENCE MANUAL 07-2009 Reference Manual page 884

Flag Operation
Serial
Communications
Unit
Reception Completed Flag
(Bit 6 of n+9 or n+19,
n = CIO 1500 + 25 x unit number)
CPU Unit
Hint
• Execute RXDU(255) to read the received data from the buffer when the Reception Completed Flag
(in the allocated DM Setup Area) is ON.
Precautions
• Further data cannot be received until the received data is read from the buffer with RXDU(255).
When the Reception Completed Flag goes ON, read that data promptly with RXDU(255) before more
data is input to the port.
• When RXDU(255) is used to read data that was received at one of the Serial Communications Unit's
ports, the port's reception buffer is cleared after RXDU(255) is executed. Consequently, RXDU(255)
can not be executed repeatedly to read a block of data in parts.
• RXDU(255) can be used only for a Serial Communications Unit's serial port that has been set to no-
protocol mode.
• If 0 is specified for N, the Reception Completed Flag and Reception Overflow Flag will be turned OFF,
the Reception Counter will be cleared to 0, and nothing will be stored in memory.
• RXDU(255) uses a logical port (because it sends an internal FINS command) to output a receive
sequence command to a Serial Communications Unit or CS-series Serial Communications Board.
Since SEND(090), RECV(098), CMND(490), PMCR(260), and TXDU(256) also use logical ports 0 to
7, RXDU(255) cannot be executed for a logical port if that logical port is already being used by one of
those instructions or another RXDU(255) instruction.
To ensure that RXDU(255) is not executed while the logical port is busy, program the port's
Communications Port Enabled Flag (A202.00 to A202.07) as a normally open condition.
CS/CJ/NSJ Series Instructions Reference Manual (W474)
Reception processing
ON
OFF
RXDU(255)
Communications Port
ON
Enabled Flag
(A20200 to A20207 correspond to
communications ports 0 to 7.)
OFF
Writing data to the CPU Unit's
data area
End code or specified
number of bytes received.
Reception
processing
Instruction
execution
Write
processing
CPU Unit
RXDU
RXDU
3. Instructions
3
847