Honeywell 621-9939 Serial Link Module

The Honeywell 621-9939 Serial Link Module (SLM) is a communication interface module for the Honeywell IPC 620 control platform. It provides two independent serial communication channels and incorporates its own asynchronous processor with a dedicated data table, allowing communication tasks to be handled separately from the main system CPU. This architecture supports serial I/O integration while reducing processor overhead within the control system.

System Integration

The 621-9939 module is designed specifically for installation within Honeywell IPC 620 system racks. It can only be installed in slot L and/or slot M of the chassis.

A maximum of two Serial Link Modules can be installed in a single rack, enabling expansion of serial communication capacity while maintaining compliance with IPC 620 hardware configuration requirements.

Communication Architecture

The module controls two independent serial communication channels. An onboard asynchronous processor manages communication activity locally and maintains a dedicated internal data table for serial data exchange.

By handling communication processing independently, the module reduces the workload placed on the primary controller and provides a structured interface between the CPU and connected serial devices.

Wiring and Network Requirements

Proper communication line installation requires a 200 Ohm termination resistor at each end of the communication trunk line. Correct line termination helps maintain signal integrity and reliable data transmission.

Honeywell recommends the use of high-quality shielded twisted-pair communication cable such as Belden 9729 or an equivalent cable with similar characteristics.

Diagnostics and Field Connections

The front panel incorporates five diagnostic LEDs to provide immediate status indication during commissioning and maintenance activities. These indicators support monitoring of module power, communication status with the system CPU, and serial port transmission activity.

Field wiring is terminated through industrial terminal block connectors, providing secure connections for remote I/O networks, operator interfaces, and other serial communication devices.

Technical Specifications

Installation Considerations

The module should only be installed in the designated IPC 620 rack positions. When deploying serial communication networks, proper trunk-line termination and cable selection are important to ensure stable operation and communication reliability.

System designers should verify rack slot availability and communication channel requirements before configuring multiple Serial Link Modules within the same chassis.

Frequently Asked Questions

Q: Which IPC 620 rack slots support the 621-9939 module?

A: The module is designed for installation only in slot L and/or slot M of the Honeywell IPC 620 chassis. Installation in other rack positions is not specified for this model.

Q: How many communication channels does the module provide?

A: The 621-9939 supports two independent serial communication channels, allowing simultaneous communication with multiple serial devices or networks.

Q: Does the module use the main CPU for communication processing?

A: No. The module includes an independent asynchronous processor and dedicated internal data table that perform communication processing separately from the main system CPU.