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MELSEC-L Series Serial Communication Unit (LJ71C24)

MELSEC-L Series Serial Communication Unit LJ71C24

A serial communication unit for the standard model MELSEC-L series

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Part Number

Configured Part Number is shown.

LJ71C24

Serial Communication Unit Features

Immediate Connection for Communication With Desired Device

All you have to do is to select any device you want to communicate with from the GX Works2 communication protocol library, and you can connect to the device immediately.
1. Select the manufacturer and model (series) of the connecting device: No need to set a complex communication protocol with the connecting device. Just select from the pre-prepared communication protocol library.

Communication protocol library

Communication protocol library

2. Write a communication protocol to the unit: Write a pre-defined communication protocol to the serial communication unit. Up to 128 settings can be made per unit.

Image of writing a communication protocol

Image of writing a communication protocol

3. Execute the protocol from the ladder program: Via the ladder program you can communicate with external devices simply by executing the dedicated command for starting the communication protocol.

Image of executing the dedicated command

Image of executing the dedicated command

Easy to Create and Edit Communication Protocols

Even when a desired device is not found in the communication protocol library, an additional communication protocol can be created in easy steps.

Image of creating a communication protocol

Image of creating a communication protocol

The content of the created communication protocol can be displayed in a list and can be edited easily.

Image of editing

Image of editing

Serial Communication Unit Specifications

ItemLJ71C24LJ71C24-R2
Interfacech1RS-232 compliant (D-Sub 9P female)RS-232 compliant (D-Sub 9P female)
ch2RS-422/485-compliant (2-piece terminal block)RS-232 compliant (D-Sub 9P female)
Communication methodCircuitFull-duplex / half-duplex
MC protocolHalf-duplex
Communication protocolFull-duplex / half-duplex
Non-procedural protocol
Bidirectional protocol
Synchronization methodAsynchronous method
Transmission speed50 bps / 300 bps / 600 bps / 1,200 bps / 2,400 bps / 4,800 bps / 9,600 bps / 14.4 kbps /
19.2 kbps / 28.8 kbps / 38.4 kbps / 57.6 kbps / 115.2 kbps / 230.4 kbps
230.4 kbps can be used on the ch1 side only. (Cannot be used on the ch2 side)
The total transmission speed of the two interfaces may be used within 230.4 kbps.
If the send/receive data monitoring function is used, the total transmission speed of the two interfaces may be used within 115.2 kbps.
Data formatStart bit1
Data bit7 or 8
Parity bit1 (vertical parity) / None
Stop bit1 or 2
Access cycleMC protocolOne request is processed during END processing of the CPU unit for the C24 installed station.
(The number of scans / link scans required for this process varies depending on the specific request.)
Communication protocolIn both send and receive operations, this request is processed when the dedicated command (CPRTCL command) is executed.
Non-procedural protocolData is sent every time a send request is made, while reception of data can be made at all times.
Bidirectional protocol
Error detectionParity checkApplicable to all protocols. If applicable, select odd or even using parameters.
Checksum codeFor MC protocol or bidirectional protocol, select by parameter.
For communication protocol, whether or not a checksum code is available is determined by the selected protocol.
In the case of a non-procedural protocol, a checksum code is selected by a user-registered frame.
Transmission distance
(total extension distance)
RS-232Maximum 15 m
RS-422/485Maximum 1,200 m (total extension distance)-
Number of units occupied1
Number of occupied inputs/outputs32 points (I/O assignment: Intelligent 32 points)
5 V DC internal current consumption0.39 A0.26 A
Weight0.17 kg0.14 kg

Transmission Control

 RS-232RS-422/485
DTR/DSR (ER/DR) controlAvailableNot available
RS/CS controlAvailableNot available
CD signal controlAvailableNot available
DC1/DC3 (Xon/Xoff) control
DC2/DC4 control
AvailableAvailable
  • DTR/DSR signal control and DC code control can be selected.
Part Number
LJ71C24
Part NumberStandard Unit PriceMinimum order quantityVolume DiscountDays to Ship

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Please check the type/dimensions/specifications of the part LJ71C24 in the MELSEC-L Series Serial Communication Unit series.

Similar Part Numbers

Part Number
LJ71C24-R2
Part NumberStandard Unit PriceMinimum order quantityVolume DiscountDays to Ship

SGD 696.70

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