Mitsubishi A1SJ71QC24-R2 System-Ready Serial Communication for MELSEC-A Architecture
The Mitsubishi A1SJ71QC24-R2 is a dual-channel RS-232C/RS-422 serial communication module engineered for seamless integration within the MELSEC-A and MELSEC-AnS control system architecture. Designed to serve as the communication backbone between the CPU layer and external devices, this module enables reliable data exchange across multiple automation tiers — from field-level sensors and drives to supervisory SCADA systems and HMI panels. Its role within a layered automation architecture is not merely peripheral; it is a critical enabler of system-wide data consistency, real-time diagnostics, and long-term operational stability.
Architecture Specification Table
| Parameter |
Specification |
| System Role |
Dual-Channel Serial Communication Module (Network Layer) |
| Compatible Series |
MELSEC-A / MELSEC-AnS (A1S, A2S, A3N, A2N platforms) |
| Communication Interfaces |
RS-232C (CH1) / RS-422 (CH2) |
| Transmission Speed |
300 bps to 19,200 bps (selectable per channel) |
| Protocol Support |
MC Protocol (Format 1/4), Non-procedure, Bidirectional |
| Electrical Standard |
RS-232C: ±15V signal level; RS-422: differential balanced |
| Power Consumption |
5VDC, 0.35A (from backplane bus) |
| Installation |
MELSEC-A series base unit slot mount (A1S68B, A1S38B compatible) |
| Operating Temperature |
0°C to 55°C |
| Operating Humidity |
10% to 90% RH (non-condensing) |
| Vibration Resistance |
10–57 Hz, 0.075 mm amplitude; 57–150 Hz, 9.8 m/s² |
| Warranty |
12-Month Warranty — covered from date of shipment |
Coordinated Control System Design
In a complete MELSEC-A control system architecture, the A1SJ71QC24-R2 occupies the network communication layer, bridging the CPU processing core with downstream field devices and upstream supervisory systems. This module is typically installed alongside the A1SJCPU-S3 or A2SCPU as the central processing unit, which handles ladder logic execution and I/O scanning. The CPU communicates with the A1SJ71QC24-R2 via the internal backplane bus, enabling transparent data routing without consuming CPU scan time excessively.
The backplane itself — commonly the A1S68B (8-slot) or A1S38B (3-slot) base unit — provides the physical and electrical foundation for module integration. Power is supplied through the A1S61PN or A1S62PN power supply module, which delivers regulated 5VDC and 24VDC rails to all installed modules, including the A1SJ71QC24-R2. Stable power architecture is essential for maintaining communication integrity, particularly in environments with high electromagnetic interference.
On the I/O layer, digital input modules such as the A1SX41 (32-point DC input) and output modules like the A1SY41 (32-point transistor output) feed process signals into the CPU, while the A1SJ71QC24-R2 simultaneously handles serial data exchange with external equipment — barcode readers, weighing controllers, variable frequency drives, or third-party SCADA terminals. This parallel operation ensures that communication tasks do not interfere with real-time I/O processing.
For applications requiring network-level connectivity beyond serial communication, the A1SJ71E71-B2-S3 Ethernet interface module can be installed in an adjacent slot, enabling TCP/IP-based data acquisition alongside the RS-232C/RS-422 channels of the A1SJ71QC24-R2. This dual-protocol approach supports Contextual Integration across both legacy serial devices and modern Ethernet-enabled systems within the same control cabinet.
In redundant or high-availability architectures, the A1SJ71QBR11 MELSECNET/B data link module may be deployed to establish peer-to-peer communication between multiple MELSEC-A PLCs, while the A1SJ71QC24-R2 continues to manage local serial device communication. This layered communication strategy ensures that a failure in one communication path does not cascade into a full system outage.
For applications transitioning toward the MELSEC-Q platform, the QJ71C24N serial communication module serves as the functional successor, maintaining protocol compatibility with MC Format 1/4 while offering enhanced throughput. Engineers managing mixed-generation architectures can leverage the A1SJ71QC24-R2 in legacy AnS racks while planning a phased migration to Q-series hardware.
Application in Layered Automation Systems
The A1SJ71QC24-R2 is deployed across a wide range of industrial sectors where serial communication remains the standard interface for field devices and supervisory systems.
In manufacturing and assembly lines, the module connects MELSEC-A PLCs to torque controllers, vision inspection systems, and label printers via RS-232C, enabling real-time quality data collection without disrupting the main control scan cycle. In power distribution and substation automation, the RS-422 channel provides noise-immune long-distance communication with protection relays and energy meters, supporting IEC 60870-compatible data formats through non-procedure protocol configuration.
In petrochemical and process control environments, the module interfaces with flow computers, gas analyzers, and DCS gateways, transmitting process variables and alarm states to SCADA systems. Its wide operating temperature range and vibration resistance make it suitable for installation in field control panels near process equipment. In water treatment facilities, the A1SJ71QC24-R2 manages communication with dosing pump controllers and level transmitters, supporting continuous process monitoring with minimal maintenance overhead.
In mining and metallurgical applications, where control cabinets are subject to dust, vibration, and temperature extremes, the module’s robust electrical design and sealed connector interface ensure sustained communication reliability. For packaging and material handling lines, the bidirectional protocol mode enables handshaking with robotic arms, conveyor controllers, and checkweighers, supporting high-throughput production with synchronized data exchange.
Architecture Engineering FAQ
Q1: Is the A1SJ71QC24-R2 compatible with both A-series and AnS-series base units?
Yes. The A1SJ71QC24-R2 is designed for the MELSEC-AnS compact series and is compatible with A1S-series base units including the A1S68B and A1S38B. It is not directly compatible with the larger MELSEC-A (A2N, A3N) main base units without an appropriate extension configuration. Always verify slot availability and power budget before installation.
Q2: Can the A1SJ71QC24-R2 operate both channels simultaneously, and what protocols are supported?
Yes, both CH1 (RS-232C) and CH2 (RS-422) can operate simultaneously and independently. Supported protocols include MC Protocol Format 1 and Format 4 for PLC-to-device communication, Non-procedure mode for free-format serial data exchange, and Bidirectional mode for full-duplex communication with external controllers. Protocol selection is configured via GX Developer parameter settings without hardware modification.
Q3: What does the 12-Month Warranty cover, and how is long-term maintenance supported?
The 12-Month Warranty covers manufacturing defects and functional failures under normal operating conditions from the date of shipment. For long-term maintenance, we recommend maintaining a spare module in inventory given the MELSEC-A series’ legacy status. Our technical team provides pre-shipment functional verification, configuration documentation support, and post-sale engineering consultation to ensure continued system uptime. Replacement units are available from stock with rapid dispatch to minimize unplanned downtime.
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