Product Overview

The Allen Bradley 1790-7CMCBL CompactBlock LDX I/O Expansion Ribbon Cable is a 7 cm replacement ribbon cable used to establish the expansion connection between compatible CompactBlock LDX I/O base blocks and expansion modules. It maintains the internal connection required for additional I/O blocks to operate as part of the same distributed I/O assembly.

Unlike DeviceNet network cables, the 1790-7CMCBL is not used to connect a PLC or network scanner to a remote I/O station. Its function is limited to the interconnection of CompactBlock LDX modules. The base block handles network communication, while the ribbon cable maintains the expansion link to the additional I/O blocks.

The 7 cm cable is intended for closely positioned modules installed in a conventional horizontal arrangement. In this configuration, the base block and expansion blocks are mounted side by side in an end-to-end layout. The short cable provides the necessary connection without requiring the additional length of the 15 cm expansion cable.

For example, a machine control panel may contain a CompactBlock LDX digital input base block together with a 16-point output expansion module. The base block handles the DeviceNet connection, while the 1790-7CMCBL connects the expansion module to the main I/O assembly. This allows additional field signals to be incorporated without installing another independent network adapter.

The cable is also relevant during maintenance and replacement. Expansion ribbon cables can become damaged through improper handling, excessive bending, or mechanical interference during module installation. If the connection is interrupted, the associated expansion module may no longer communicate correctly with the base block. Replacing the damaged cable with the correct 7 cm model restores the intended physical expansion connection.

Another consideration is the distinction between the 1790-7CMCBL and the longer 1790-15CMCBL. The 7 cm version is intended for standard closely mounted expansion arrangements, whereas the 15 cm version is required for the specified vertical back-to-back mounting configuration. Selecting the correct cable length is therefore part of the physical installation planning rather than simply a matter of cable replacement.

The 1790-7CMCBL is supplied with compatible expansion modules as part of their standard expansion connection arrangement. It is also listed as a replacement accessory, with the replacement cable supplied in lots of five.

For CompactBlock LDX installations where an existing expansion connection needs replacement, the 1790-7CMCBL maintains the original short-distance module interconnection without changing the overall I/O architecture.

Technical Specifications

Product Features

• 7 cm Cable Length: Provides the short-distance connection required for closely positioned CompactBlock LDX modules.
• Expansion Module Interconnection: Connects compatible base blocks and expansion blocks within the same I/O assembly.
• Replacement Accessory: Serves as a replacement for damaged or missing CompactBlock LDX expansion ribbon cables.
• Horizontal Mounting Support: Suitable for conventional end-to-end module arrangements.
• Compact Ribbon Construction: Keeps the expansion connection within the module assembly without introducing a separate external network cable.
• DeviceNet System Compatibility: Supports expansion connections in compatible DeviceNet-based CompactBlock LDX installations.
• Standard Expansion Accessory: Included with compatible expansion modules and also available as a replacement component.
• Five-Piece Supply Lot: Replacement cables are listed in lots of five.

Working Principle

The 1790-7CMCBL functions as the physical expansion connection between CompactBlock LDX modules. Its purpose is to maintain the internal link through which an expansion block becomes part of the main I/O assembly.

The basic system arrangement is:

PLC Controller → DeviceNet Scanner → CompactBlock LDX Base Block → 1790-7CMCBL → Expansion I/O Module

Establishing the Expansion Connection

The base block acts as the main interface between the distributed I/O assembly and the DeviceNet network. When an additional input or output module is installed, the ribbon cable connects it to the existing base block or another compatible expansion block.

The cable maintains the required expansion connection, allowing the additional I/O points to be incorporated into the assembly.

For example, when a machine requires more digital output channels, a compatible output expansion block can be installed beside the existing base block. The 1790-7CMCBL connects the two units, allowing the expanded arrangement to operate through the existing network interface.

Horizontal Module Arrangement

The 7 cm cable is intended for the conventional horizontal installation configuration.

In this arrangement, the base block and expansion modules are mounted side by side in an end-to-end layout. The short ribbon cable bridges the expansion connection between adjacent blocks.

This configuration is commonly used in industrial control panels where the modules can be arranged in a continuous row along a DIN rail or mounting panel.

Expansion Data Transfer

The ribbon cable does not function as an independent DeviceNet communication cable. Instead, it maintains the internal expansion connection between the modules.

The base block handles communication with the DeviceNet scanner and PLC controller. The expansion arrangement allows the additional I/O points to participate in the same control system.

For instance, a packaging machine may use one base block for the main network connection and additional expansion blocks for product-detection sensors and auxiliary output circuits. The ribbon cable maintains the connection between the modules, while the controller processes the resulting I/O information through the base block.

Cable Length Selection

The 1790-7CMCBL and 1790-15CMCBL serve different installation requirements.

The 7 cm version is intended for standard horizontal module arrangements. When the modules need to be installed vertically in a back-to-back configuration, the longer 15 cm cable is required. The longer cable also allows up to 7 cm of spacing between blocks in the specified arrangement.

Choosing the correct cable prevents unnecessary tension on the expansion connection and helps maintain the intended physical installation.

Maintaining Connection Integrity

Both ends of the ribbon cable must be correctly positioned and securely connected. A loose connection, damaged conductor, or improperly routed cable can interrupt the expansion link.

During maintenance, technicians should inspect the cable for deformation, damaged sections, and signs of mechanical stress. If the cable is defective, replacing it with the correct catalog number helps restore the connection between the CompactBlock LDX modules.

Role in the CompactBlock LDX Control Architecture

The Allen Bradley 1790-7CMCBL serves as an internal connection accessory within the CompactBlock LDX distributed I/O architecture. It allows compatible expansion blocks to connect to the main I/O assembly while maintaining the existing DeviceNet communication structure.

A typical system arrangement follows this structure:

PLC Controller → DeviceNet Scanner → CompactBlock LDX Base Block → 1790-7CMCBL → Expansion I/O Module → Field Devices

In a typical machine automation installation, the base block communicates with the PLC through DeviceNet. Additional expansion blocks connect to the existing assembly through their ribbon cable interfaces.

The 1790-7CMCBL maintains the short-distance connection required for adjacent modules. This allows the system to add input and output capacity without introducing another independent network connection for every expansion block.

Its role is particularly relevant during system maintenance, where replacing a damaged ribbon cable can restore the expansion connection without requiring changes to the PLC program or DeviceNet network configuration.

Industrial Applications

Installation and Maintenance

1. Verify the Cable Model: Confirm that Allen Bradley 1790-7CMCBL is the required 7 cm CompactBlock LDX expansion ribbon cable.
2. Check Module Compatibility: Ensure that the base block and expansion module support the CompactBlock LDX expansion connection.
3. Inspect the Cable: Examine the ribbon cable for damaged conductors, deformation, cracks, or other signs of mechanical wear.
4. Plan the Module Arrangement: Confirm that the modules will be installed in the conventional horizontal end-to-end configuration.
5. Isolate the Power Supply: Disconnect the relevant system power before connecting or removing the expansion ribbon cable.
6. Position the Expansion Blocks: Mount the base block and expansion modules in their intended positions on the DIN rail or panel.
7. Connect the Ribbon Cable: Insert the cable into the designated expansion interfaces, ensuring that both ends are correctly aligned and seated.
8. Check Cable Routing: Ensure that the ribbon cable is not twisted, sharply bent, pinched, or subjected to unnecessary mechanical tension.
9. Verify Module Positioning: Check that the adjacent blocks are positioned correctly and that the cable reaches both expansion interfaces without strain.
10. Secure the Installation: Confirm that the modules are firmly mounted and that the cable is not carrying the mechanical load of the assembly.
11. Test the Expansion Connection: Restore power and verify that the connected expansion module is recognized and its assigned I/O points operate correctly.
12. Document the Replacement: Record the cable model, installation arrangement, connected expansion modules, and any maintenance performed.

Compatible System Components

Recommended Related Models

Key Advantages

• Provides a 7 cm expansion connection for adjacent CompactBlock LDX modules.
• Maintains the internal connection between compatible base blocks and expansion modules.
• Supports conventional horizontal end-to-end mounting.
• Serves as a replacement for damaged or missing expansion ribbon cables.
• Maintains the existing DeviceNet-based I/O architecture.
• Eliminates the need for a separate external network cable between expansion blocks.
• Supplied in replacement lots of five cables.

Technical FAQs

What is the main function of the Allen Bradley 1790-7CMCBL?

The 1790-7CMCBL connects compatible CompactBlock LDX base blocks and expansion modules through their internal expansion interfaces. It maintains the physical connection required for additional I/O blocks to operate as part of the same distributed I/O assembly. It is not a standalone DeviceNet communication cable.

What is the difference between the 1790-7CMCBL and the 1790-15CMCBL?

The main difference is cable length and installation application. The 1790-7CMCBL is a 7 cm replacement ribbon cable intended for standard horizontal module arrangements. The 1790-15CMCBL is a longer 15 cm cable required for the specified vertical back-to-back mounting configuration. The longer version also accommodates up to 7 cm of spacing between blocks.

Is the 1790-7CMCBL included with CompactBlock LDX expansion modules?

Yes. The 7 cm ribbon cable is included with compatible expansion modules as part of their standard connection arrangement. It is also available separately as a replacement accessory, supplied in lots of five.

Can a damaged 1790-7CMCBL affect the operation of an expansion module?

Yes. The ribbon cable maintains the expansion connection between the base block and the additional I/O module. If the cable is damaged, incorrectly positioned, or not securely connected, the expansion module may not operate or communicate as expected. During troubleshooting, inspect both cable ends and replace the cable if physical damage is identified.