2MLL-CH2A | Honeywell | Serial Communication Interface Module

The Honeywell 2MLL-CH2A, also cataloged as the 2MLL-CH2A Serial Communication Interface Modules, operates as a dedicated hardware component for serial data protocol handling within Master-K platform PLC networks. It establishes dual asynchronous channels to route field device data via RS-232C and RS-422/485 serial interfaces directly into the central processor memory map.

Hardware Specifications

4-20 mA HART Loop Protocol & DCS Integration

While operating primarily as an asynchronous serial processor, the module enables protocol mapping interfaces that interact with field instrument networks. Integrated channel-to-channel isolation safeguards backplane communications from electrical noise, common-mode ground potential shifts, and transient surges originating on external RS-422/485 multidrop lines. This isolation barrier prevents loop corruption and maintains signal processing integrity across long line distances when transmitting digitized process values from legacy 4-20 mA transmitters or serial gateway bridges.

Frequently Asked Questions

Q: What is the backplane current draw for the 2MLL-CH2A module during active transmission?

A: The module draws a continuous current of 310 mA from the internal 5 VDC backplane bus power supply. Ensure the base rack power supply unit has sufficient overhead capacity prior to adding channels.

Q: How are network parameters and protocol selections assigned to the dual serial ports?

A: Parameter assignments including baud rate (300 to 115200 bps), data bits (7 or 8), parity, and protocol modes (Modbus RTU/ASCII or P2P) are configured via the SoftMaster-NM programming environment and flashing memory down to the module interface.

Q: What topology configuration options exist for the RS-422/485 channel?

A: The RS-422/485 port supports 1:1, 1:N, and N:M multi-drop networking configurations with station numbers assigned from 0 to 31, servicing up to 32 network nodes across a maximum distance of 500 m.

Field Installation Guidelines

1. Power down the PLC rack chassis completely before inserting or removing the module from the backplane slot.
2. Verify that shield wires for RS-422/485 serial cables are grounded at a single point to prevent ground loops from introducing serial framing errors.
3. Keep RS-232C cable runs within the 15 m physical length limit to avoid signal attenuation and parity faults at higher baud rates.
4. Ensure terminating resistors (typically 120 ohm) are enabled or connected across the physical end-nodes of the RS-485 differential bus line.