Omron SYSMAC CJ - REFERENCE MANUAL 08-2008 Reference Manual page 1037

Serial Communications Instructions
Flags
Precautions
Name Label
Error Flag ER
RXD(235) can be used only for the CPU Unit's RS-232C port or one of the
Serial Communications Board's serial ports. In addition, the port must be set
to no-protocol mode.
The following receive message frame format can be set in the PLC Setup (for
the CPU Unit's RS-232C port) or the allocated DM Setup Area (for the Serial
Communications Board's ports).
• Start code: None or 00 to FF hex
• End code: None, CR+LF, or 00 to FF hex. If no end code is specified, the
number of bytes to received is set from 00 to FF hex (1 to 256 decimal; 00
specifies 256 bytes).
The Reception Completed Flag (note 1) will turn ON when the number of
bytes specified in the PLC Setup (for the CPU Unit's RS-232C port) or the
allocated DM Setup Area (for the Serial Communications Board's ports) has
been received. When the Reception Completed Flag turns ON, the number of
bytes in the Reception Counter (note 2) will have the same value as the num-
ber of receive bytes specified in the PLC Setup or the allocated DM Setup
Area. If more bytes are received than specified, the Reception Overflow Flag
(note 3) will turn ON.
If an end code is specified in the PLC Setup or the allocated DM Setup Area,
the Reception Completed Flag (note 1) will turn ON when the end code is
received or when 256 bytes of data have been received.
Reception will be stopped if 259 bytes of data are received. If more data is
input after that, the Overrun Error Flag (note 5) and Transmission Error Flag
(note 6) will turn ON.
When more data is input to the Serial Communications Board's serial port
than is specified in N, that data will be discarded when RXD(235) is executed.
In contrast, extra data input to the CPU Unit's RS-232C port will not be dis-
carded when RXD(235) is executed.
When RXD(235) is executed, data is stored in memory starting at D, the
Reception Completed Flag (note 1) will turn OFF (even if the Reception Over-
flow Flag (note 3) is ON).
Operation
ON if the CPU Unit's RS-232C port is specified as the
send port, but no-protocol mode is not set in the PLC
Setup.
ON if one of the Serial Communication Board's serial
ports is specified as the send port, but no-protocol mode
is not set in the port's allocated DM Setup Area.
ON if the value of C is not within range.
ON if the value for N is not between 0000 and 0100 hex.
ON (ER Flag in interrupt tasks) if a TXD(236) or
RXD(235) instruction is being executed for the Serial
Communications Board in the cyclic task, the cyclic task
is interrupted, and another TXD(236) or RXD(235)
instruction is executed for the Serial Communications
Board in the interrupt task. (See note.)
ON if a RXD(235) was executed for a serial port on a
Serial Communications Board that was being restarted.
Note The Error (ER) Flag will turn ON immediately after
another TXD(236) or RXD(235) instruction in the
interrupt task.
OFF in all other cases.
Section 3-24
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