The Allen-Bradley 1756-L85E, also cataloged as the 1756-L85 Controller, operates as a dedicated hardware component for high-speed logic execution and multi-axis CIP Motion processing within EtherNet/IP control networks.

Catalog Designation & Platform Variants

The base model 1756-L85 designates the core central processing unit within the ControlLogix 5580 hardware platform. The letter suffix "E" identifies the integration of an embedded 1 Gbps RJ45 Ethernet communication port on the front panel. The numerical designation "85" specifies the internal memory tier, providing 40 MB of user application memory for program execution, tag storage, and controller task organization.

Processing Unit Hardware Specifications

High-Speed Backplane Bus & Network Synchronization

The Allen-Bradley 1756-L85E utilizes high-velocity backplane bus communication across the 1756 chassis structure, maximizing data throughput to local I/O modules and network bridges. Operating within Profinet / EtherNet/IP deterministic networks, the controller enforces real-time I/O scanning and synchronized motion axis execution. Strict firmware flash compatibility ensures stable system task scheduling and deterministic handshakes between memory registers and field instrumentation.

Package Component List

• 1 x Allen-Bradley 1756-L85E ControlLogix 5580 Controller Module
• 1 x 1784-SD2 2 GB Secure Digital (SD) Card (pre-installed)

Mechanical Installation & Wiring Protocols

• Chassis Slot Insertion
  • Align the controller module circuit board with the top and bottom guides of any slot in a 1756 chassis. Press the unit firmly into the backplane until the upper and lower housing latches click into place.
• Earth Grounding Integrity
  • Ensure the 1756 chassis ground lug connects to the central cabinet functional earth bar using heavy gauge copper wire (minimum 14 AWG) to establish low-impedance grounding.
• Network Interface Wiring
  • Route Category 6 STP Ethernet cables away from high-voltage power conduits and variable frequency drive outputs to prevent electromagnetic interference.
• Memory Card Retaining Latch
  • Verify that the front SD card access door is fully closed during operation to protect the card slot pins from environmental debris and static discharge.

Technical Engineering FAQ

• What is the hot-swapping restriction for inserting the module into an active chassis?

  The module supports Removal and Insertion Under Power (RIUP). It can be installed into or removed from an active 1756 backplane without interrupting adjacent operational modules.

• What current does the controller draw from the 5.1 VDC backplane power rail?

  The controller draws 1.2 A from the 5.1 VDC rail of the chassis power supply during normal processing and network communication operations.

• How does network latency perform during heavy CIP Motion execution?

  The embedded 1 Gbps Ethernet port offloads network layer processing directly on the CPU hardware, maintaining sub-millisecond motion cycle synchronization without latency spikes.

• Does firmware flashing erase the stored user program in the controller?

  Yes, flashing firmware clears active volatile RAM. Non-volatile flash storage or SD card image restoration is required to restore program code after flashing.

• How should Ethernet cable shielding be grounded at the controller connection point?

  Ground the Ethernet cable shield at the cabinet entry gland plate or network switch end, maintaining continuous shielding to the controller metallic RJ45 socket.

• What happens to local I/O states if the controller undergoes an unrecoverable fault?

  Outputs transition immediately to their configured fault state (off, on, or hold last state) as defined within the local I/O module configuration parameters.

• Is an internal battery required to retain user application program memory?

  No, the unit uses energy storage capacitors and internal non-volatile flash memory to preserve data during total power loss without using lithium batteries.

• What minimum bend radius must be maintained for the front Ethernet patch cable?

  Maintain a minimum bend radius of four times the outer cable diameter to avoid conductor displacement and physical strain on the RJ45 port assembly.