The Modicon PC-A984-120 is a versatile, compact CPU module from the legacy 984 series, designed for small to medium-scale industrial control applications. Known for its rugged construction and deterministic logic execution, this PLC processor provides a cost-effective solution for discrete manufacturing, water treatment, and basic process automation where space is a primary constraint.

Technical Functionality

The A984-120 utilizes the standard 984 Ladder Logic (LL) programming language, ensuring compatibility with a wide range of existing Modicon software tools. It manages I/O scanning and logic solving within a single compact housing, communicating with distributed I/O modules via the Modbus or Modbus Plus protocols. Its internal memory architecture is optimized for fast boolean operations, making it highly effective for high-speed machine control.

 

Key Specifications

 

Operational Precautions

• Memory Protection: The user program is stored in volatile RAM backed by a lithium battery. Replace the battery every 1–2 years while the PLC is powered up to avoid losing the application logic.
• Communication Addressing: When configuring the Modbus port, ensure the Slave ID and Baud Rate match the connected HMI or SCADA interface; incorrect parity settings are a common cause of “Time-Out” errors.
• Firmware Integrity: This legacy module uses EPROM or Flash-based executive firmware. Avoid exposing the module to extreme magnetic fields or high-voltage transients that could corrupt the internal operating system.

 

Common Questions Q&A

Q: Can the A984-120 be programmed with modern Schneider Electric software? A: While originally programmed with Modsoft or Proworx, many configurations can be imported into Schneider Electric’s Unity Pro (now Control Expert) using specialized conversion utilities, though direct hardware support is limited.

Q: Does it support remote I/O expansion? A: Yes, through the Modbus Plus port, the A984-120 can serve as a master to remote I/O drops, significantly extending the physical reach of the control system beyond the local rack.

 

Recommended Similar Models

1. AS-984-145: A more powerful version of the 984 compact series with expanded memory.
2. PC-E984-258: A high-end 984 processor designed for larger I/O counts and complex math.
3. AS-P984-685: A slot-mount processor variant for the larger Modicon 800-series housing.
4. 140CPU11302: A Quantum series CPU, the modern successor for migration paths.
5. BMXP342020: A contemporary Modicon M344 processor for modernizing legacy 984 systems.

Technical documentation and inventory details for the Modicon PC-A984-120 are available through our current PLC and industrial control catalog.