Configured for SERCOS motion communication in a ControlLogix chassis, the Allen-Bradley 1756-M08SEG (1756-M08SEG Generic Servo Module) provides an 8-axis interface for Extended Pack Profile compliant SERCOS drives. The module supports 4 Mbps and 8 Mbps SERCOS data rates.

Model and Function

The 1756-M08SEG is identified by Rockwell Automation as a ControlLogix SERCOS Generic Servo Module, Series A. It provides up to 8 axes per module and supports up to 32 axes within a controller configuration. The module uses the SERCOS interface for communication with compatible servo drives.

The module is intended for drives using the AXIS_GENERIC_DRIVE data type and Extended Pack Profile. Motion communication is carried over a fiber-optic SERCOS connection rather than conventional discrete wiring.

Hardware Specifications

Rockwell Automation technical documentation identifies the 1756-M08SEG as an 8-axis SERCOS interface module for Extended Pack Profile compliant applications.

SERCOS Motion Interface

The 1756-M08SEG provides a digital fiber-optic SERCOS link between the ControlLogix controller and compatible servo drives. Rockwell Automation specifies 4 Mbps and 8 Mbps communication rates for the SERCOS interface.

For the 1756-M08SEG, published technical data specifies the following SERCOS cycle relationships:

• At 4 Mbps, 0.5 ms supports up to 2 drives where applicable, 1 ms supports up to 4 drives, and 2 ms supports up to 8 drives.
• At 8 Mbps, 0.5 ms supports up to 4 drives where applicable, 1 ms supports up to 8 drives, and 2 ms supports up to 16 drives.
• The module provides 8 available axes.
• The controller configuration can contain up to 32 axes.
• The module is associated with the AXIS_GENERIC_DRIVE data type for generic SERCOS drive operation.

The SERCOS connection uses fiber-optic cabling. The communication path therefore does not use the conventional copper signal wiring normally associated with discrete drive interfaces.

ControlLogix Backplane and Motion Configuration

The module receives its operating power through the ControlLogix chassis backplane. The supplied specifications list 760 mA at 5 VDC and 2.5 mA at 24 VDC for backplane current.

The specified 6.2 W value represents power dissipation rather than a field-side power output. The module does not provide an external drive power supply.

The 1756-M08SEG is a chassis-based module. Installation requires a compatible ControlLogix chassis and an available module position. Published compatibility information includes 1756-A4, 1756-A7, 1756-A10, 1756-A13, and 1756-A17 chassis.

Ordering Information

• 1 x Allen-Bradley 1756-M08SEG Generic Servo Module
• Catalog number: 1756-M08SEG
• Series: A
• Module function: 8-axis SERCOS Generic Servo Module
• Fiber-optic SERCOS cables are not included unless separately specified.
• ControlLogix chassis, power supply, servo drives, and programming software are not included unless separately specified.

Installation and Wiring

Chassis Installation

• Install the module in a compatible ControlLogix chassis slot.
• Verify the available chassis power capacity against the module backplane current requirements.
• Install the chassis and power supply according to the applicable ControlLogix installation documentation.
• Follow static-control procedures when handling the module.

SERCOS Connection

• Connect the SERCOS interface using the specified fiber-optic communication path.
• Keep fiber-optic cables away from excessive bending, crushing, and mechanical stress.
• Inspect optical connectors for contamination before connection.
• Verify the SERCOS ring connection before initiating motion.

Configuration

• Configure the module for the required SERCOS data rate.
• Verify that connected drives support the required SERCOS profile.
• Use the applicable generic drive data type for the 1756-M08SEG configuration.
• Confirm axis count and cycle-time requirements before commissioning.

Frequently Asked Questions

• How many axes does the 1756-M08SEG support?

  The module provides up to 8 axes. A ControlLogix controller configuration can support up to 32 axes according to the supplied specifications.

• What communication protocol does the module use?

  The 1756-M08SEG uses SERCOS communication over a digital fiber-optic link for communication with compatible servo drives.

• What SERCOS data rates are available?

  The specified communication rates are 4 Mbps and 8 Mbps. The applicable cycle time and supported drive count depend on the selected rate.

• What is the 5 VDC backplane current?

  The specified backplane current at 5 VDC is 760 mA. This value should be included when calculating the ControlLogix chassis power load.

• Does the module require a separate field power supply?

  No external field power input is specified for the module. Operating power is supplied through the ControlLogix chassis backplane.

• What type of cable is used for SERCOS communication?

  The SERCOS interface uses fiber-optic communication. Conventional copper Ethernet or discrete signal wiring is not used for the SERCOS ring.

• Does the 1756-M08SEG use the same function as the 1756-M08SE?

  No. The 1756-M08SEG is the Generic Servo Module version and is associated with Extended Pack Profile compliant drives and AXIS_GENERIC_DRIVE configuration.

• Does the module have firmware?

  Yes. Rockwell Automation provides firmware for the 1756-M08SEG family. Firmware compatibility should be checked against the controller and motion software configuration before an update.