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Serial Communications Instructions Section 3-23
3-23 Serial Communications Instructions
This section describes instructions used for serial communications.
3-23-1 Serial Communications
There are two types of serial communications instruction. The TXD(236),
RXD(235), TXDU(256), and RXDU(255) instructions send and receive data in
no-protocol (custom) communications with an external device. PMCR(260)
sends and receives data using user-defined protocols with an external device.
The difference is shown in the following tables.
Note (1) The TXD(236) and RXD(235) instructions transfer data only through a
port on a Serial Communications Option Board.
(2) The TXDU(256) and RXDU(255) instructions transfer data only through
a CJ-series Serial Communications Unit (Ver. 1.2 or later)
(3) The PMCR(260) instructions transfers data only through a CJ-series Se-
rial Communications Unit.
Instruction Mnemonic Function code Page
PROTOCOL MACRO PMCR 260 806
TRANSMIT TXD 236 815
RECEIVE RXD 235 820
TRANSMIT VIA SERIAL COMMU-
NICATIONS UNIT
TXDU 256 825
RECEIVE VIA SERIAL COMMU-
NICATIONS UNIT
RXDU 255 833
CHANGE SERIAL PORT SETUP STUP 237 841
Instructions Communications frames Function
TXD(236),
RXD(235),
TXDU(256),
and
RXDU(255)
Sends or receives data in one direction only.
A send delay can be set.
PMCR(260) The following type of frames (messages) can be created to
meet the requirements of the external device.
Up to 16 steps can be defined for sending
and receiving.
Steps can be changed and retry processing
performed based on responses.
Communications monitoring times can be
set.
Symbols can be read/written for the PLC.
Repeat symbols can be used.
Other.
Data Data
Data Data
Only End Code
Data Data
Any of the following can be used.
No Start or End Code
Start and End Code
Only Start Code CR+LF End Code
Start and CR+LF End Code
Header Address
Data
Error check
Terminator
Communications steps
can be created.
I/O memory
Read/write
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