Serial communication module (QJ71C24N / QJ71C24N-R2 / QJ71C24N-R4)

Overview

Serial communication module family for MELSEC-Q series PLCs providing isolated serial ports for connection of RS-232 and RS-422/485 devices. Models differ by port count and interface type: QJ71C24N offers RS-232 1ch and RS-422/485 1ch; QJ71C24N-R2 offers RS-232 2ch; QJ71C24N-R4 offers RS422/485 2ch. Communication speed and reach: baud rates up to 230.4 kbps and distance up to 1200 m (for serial network links). Protocol and data handling: supports the MC protocol, can store up to 128 predefined protocols per module, and can perform multiple block batch read/write of up to 960 words from QCPU device memory. Predefined-protocol enablement is configuration-dependent: "Supported by QJ71C24N (-R2/R4) with the function version B and a serial number whose first 5 digits are 11062 or higher; Supported by products with the first five digits of the QJ71E71-100 product number of 15042 or later.", indicating firmware/serial-number requirements for full protocol feature availability. Use this module to add serial communications to a MELSEC-Q PLC rack for integrating serial peripherals and legacy devices that communicate over RS-232 or multi-drop RS-422/485 networks. Choose the base QJ71C24N when a mix of one RS-232 port and one RS-422/485 port is required, QJ71C24N-R2 for two RS-232 links, or QJ71C24N-R4 for two RS-422/485 links; select the RS-422/485 variants for longer runs or multi-drop topologies up to 1200 m. Typical deployment contexts include industrial automation and manufacturing control systems where deterministic MC-protocol exchanges, predefined protocol handling (up to 128 protocols), and batch transfers of controller memory (up to 960 words) are needed; verify module firmware/function version and serial-number requirements before relying on predefined-protocol features.