Product Details

Modicon AS-C921-101 is a robust communication processor module and reliable multi-port modbus interface designed for Modicon 984A and 984B controller racks, also known as the C921 comm card in legacy Gould / AEG Modicon product lines. This 984 series comm card offloads serial communication tasks from the main CPU and provides three independent Modbus RTU ports plus a dedicated ASCII channel, supporting simultaneous connection of programming tools, operator panels, printers, display terminals and multiple Modbus slave nodes. It carries built-in 16 digital input and 8 digital output channels, integrating basic discrete signal handling together with communication management. The module plugs directly into the dedicated 984 series backplane and draws 5 VDC power through the rack bus, with front removable cover for easy access to Port 1 and the ASCII interface, while Port 2 and Port 3 are arranged on the bottom edge of the unit. Equipped with status LEDs for each channel, it allows fast diagnosis of port activity, transmission errors and module faults. With conformal coated PCB and industrial vibration resistance, this communication processor module can run continuously in noisy, dusty process environments. As a discontinued legacy spare, this multi-port modbus interface serves as a drop-in replacement to restore multi-channel serial communication for ageing Modicon 984 automation racks.

Basic Parameters

Brand: Modicon (Gould, AEG, Schneider legacy)

Model: AS-C921-101, also named C921 Communication Processor

Product Type: Multi-Port Communication Processor Module

Compatible Rack: Modicon 984A / 984B controller backplane

Power Supply: 5 VDC via backplane, 250 mA consumption

Modbus Ports: 3 independent Modbus RTU serial ports

Auxiliary Port: Dedicated ASCII port for printer, display and P964 / P965 data panel

Onboard I/O: 16 digital inputs, 8 digital outputs

Mounting: Single-slot rack insertion

Indicator: Front LED for power, port activity and fault diagnosis

Operating Temperature: -10°C to 50°C

Relative Humidity: 10%–95%, non-condensing

Shock Resistance: 10 g for 11 ms

Product Status: Discontinued, end of original production

Net Weight: Approximately 1.45 kg

Supported Functions

This communication processor module manages all Modbus and ASCII serial traffic for the host 984A or 984B PLC. The multi-port modbus interface polls multiple Modbus slave devices within one scan cycle and transmits real-time discrete and analog process data between the main CPU and remote field equipment. This 984 series comm card supports program upload and download from programming terminals, outputs text data to ASCII printers and drives legacy operator display panels. It monitors transmission errors, parity faults and port conflicts, and sends diagnostic status back to the main controller. If serial communication is interrupted, it preserves the last valid data snapshot to avoid sudden process disturbance. It cooperates with other 984 series CPU, discrete and analog modules to build a multi-drop serial automation network for batch and continuous process control.

Core Functions

As a dedicated offload comm processor, this communication processor module acts as a serial gateway for the Modicon 984 platform, freeing the main CPU from heavy protocol processing. Its three Modbus ports enable parallel communication with separate device groups, and the native ASCII channel supports older peripheral hardware that cannot run Modbus. This multi-port modbus interface works as a direct spare to rebuild stable multi-channel serial communication for ageing Modicon 984 automation racks.

Hardware Specifications & Environmental Features

Operating Temperature: -10°C ~ +50°C

Storage Temperature: -20°C ~ +70°C

Relative Humidity: 10%–95%, non-condensing

Housing: Heavy-duty single-slot metal framed rack module

Protection: Onboard transient suppression, ESD protection for serial lines

Anti-interference: Filtered serial circuits, vibration reinforced PCB with conformal coating

Compatibility: Modicon 984A, 984B controllers, Modbus RTU slave devices, legacy ASCII peripherals

Industry Applications: Applied in legacy petrochemical distributed control, old paper making production automation, material handling conveyor lines, packaging and textile machinery, water treatment remote signal collection and large conveyor remote I/O control racks.

Note: Confirm 984A / 984B rack compatibility, Modbus baud rate and parity setting, port assignment and ASCII peripheral wiring before ordering.

This is from our current stock.

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