Honeywell 2MLL-C42B 2-Channel RS-422/RS-485 Serial Communication Module

Product Overview

The Honeywell 2MLL-C42B is a 2-channel RS-422/RS-485 serial communication module for the MasterLogic-200 (ML200) PLC system. It enables robust, noise-immune serial data exchange between the ML200 CPU and third-party devices such as variable frequency drives, weigh scales, barcode readers, and legacy instrumentation. Supporting Modbus RTU/ASCII master and slave functions, it serves as a versatile fieldbus gateway for mixed-vendor automation architectures.

Key Specifications

• Product Type: Serial Communication Module (RS-422/RS-485)
• Series: MasterLogic-200 / ML200
• Channels: 2
• Interface: RS-422 / RS-485 (software selectable)
• Isolation: 1500V between channels and communication lines
• Supported Protocols: Modbus RTU, Modbus ASCII, dedicated protocol, user-defined protocol
• Baud Rate: 300 bps to 115,200 bps
• Data Format: 7/8 data bits, 1/2 stop bits, odd/even/none parity
• Transmission Distance: Up to 1,200 meters (RS-422 at 9,600 bps)
• Connection: 9-pin D-sub connector (per channel)
• Current Consumption: 40 mA (from 5V internal bus)
• External Power: DC 24V (20.4–28.8V)
• Dimensions (W x H x D): 27.4 mm x 90 mm x 70 mm
• Weight: Approx. 90 g
• Operating Temperature: 0°C to +55°C

Features & Benefits

• Dual isolated channels — run two independent serial networks from one module, reducing hardware count by 50%
• RS-422/RS-485 selectable — software-configurable interface type eliminates the need for separate modules
• 1500V galvanic isolation — protects the CPU from ground potential differences and electrical noise on long cable runs
• Modbus RTU/ASCII native support — built-in master and slave functions eliminate custom protocol programming
• Long-distance capability — 1,200 meter range enables connection to remote field devices without repeaters

Typical Applications

• VFD parameter read/write and status monitoring
• Weigh scale and load cell indicator integration
• Barcode scanner and RFID reader communication
• Legacy PLC and DCS gateway integration
• Remote terminal unit (RTU) communication in SCADA systems
• Multi-drop Modbus networks with up to 32 devices per channel

Installation Guide

1. Select RS-422 or RS-485 mode — in SoftMaster, configure each channel for point-to-point (RS-422) or multi-drop (RS-485) operation.
2. Install in I/O slot — mount the 2MLL-C42B in any available ML200 I/O slot.
3. Connect 24V external power — wire DC 24V to the external power terminals for the interface drivers.
4. Wire serial network — connect TX+, TX-, RX+, and RX- (RS-422) or A/B (RS-485) using twisted-pair shielded cable. Ground the shield at one end only.
5. Configure protocol in SoftMaster — set baud rate, data format, and protocol type (Modbus RTU master/slave or dedicated protocol).
6. Test communication — use the SoftMaster monitor function to verify data register exchange with the connected device.

FAQ

Q: What is the difference between 2MLL-C42B and 2MLL-C42A?
A: The 2MLL-C42B is the standard RS-422/RS-485 2-channel module. The 2MLL-C42A is a variant with potentially different firmware or connector orientation. Both support identical electrical specifications and protocols. Verify your system BOM for the exact suffix required.

Q: Can I use this for RS-232C devices?
A: No. For RS-232C applications, use the 2MLL-C22A (2-channel RS-232C) or 2MLL-CH2A (1ch RS-232C + 1ch RS-422) module.

Q: What is the maximum number of devices per RS-485 channel?
A: RS-485 supports up to 32 devices per channel (1 driver + 31 receivers). For networks with >32 devices, use RS-485 repeaters or split into multiple channels.

Q: Does this module support protocol conversion?
A: The 2MLL-C42B supports Modbus RTU/ASCII natively. For protocol conversion (e.g., Modbus to Profibus), use the 2MLL-PMEA (Profibus Master) or 2MLL-PSEA (Profibus Slave) modules.

Selection Tips

• Select 2MLL-C42B for RS-422/RS-485 serial communication with drives, scales, and barcode readers.
• If you need RS-232C instead, choose 2MLL-C22A (2-channel RS-232C).
• For mixed RS-232C and RS-422 on one module, select 2MLL-CH2A.
• Always use twisted-pair shielded cable for RS-422/RS-485 runs >100 meters to prevent electromagnetic interference.
• Verify your termination resistor requirements for RS-485 multi-drop networks to prevent signal reflections.