The Allen-Bradley 1771-DB, also cataloged as the 1771-DB Basic Module, operates as a dedicated hardware component for custom ASCII string processing and serial communication execution within PLC-5 I/O chassis architecture.

Serial Interface & Functional Designator Breakdown

The Allen-Bradley 1771-DB module occupies a single slot in any 1771 I/O chassis. It provides dedicated serial ports including DH485, PRT1, and PRT2 for direct interfacing with serial printers, ASCII terminals, and barcode readers. The internal coprocessor executes BASIC language algorithms independent of the main controller sweep, offloading ASCII manipulation tasks from the primary processor.

Engineering & Physical Parameters

Backplane Integration & Data Exchange Mechanics

The module communicates with the PLC-5 processor across the 1771 backplane bus using block transfer read (BTR) and block transfer write (BTW) instructions. Communication streams bridge serial protocols with network architectures like Profinet / EtherNet/IP deterministic networks via controller gateway modules. Firmware flash compatibility maintains program execution synchronization and enables flexible I/O density scaling within legacy 1771 chassis racks.

Package Delivery Contents

• 1 x Allen-Bradley 1771-DB Basic Module Assembly
• 1 x Field Wiring Arm
• 1 x Instruction Sheet

Field Cabinet Installation Procedures

• De-energize the 1771 chassis backplane supply before inserting or removing the module from the rack slot.
• Align the circuit board with the chassis card guides and push firmly until the locking latch engages the chassis frame.
• Wire serial communication lines using shielded twisted-pair cables connected to the port screw terminals.
• Connect cable drain wires to the chassis protective earth ground terminal to suppress electromagnetic interference.
• Maintain minimum clearances around the 1771 rack to ensure ambient enclosure temperatures remain between 0 and 60 deg C.

Field Engineering FAQ

• What backplane current does the 1771-DB module draw from the 1771 chassis power supply?

  The 1771-DB module draws a maximum current of 0.75 A at 5 VDC directly from the backplane power rail.

• What communication ports are available on the front interface panel of the module?

  The module provides three communication ports labeled DH485, PRT1, and PRT2 for serial device connectivity.

• Can the 1771-DB module be removed or inserted while the rack power is turned on?

  No, removing or inserting the module while the backplane is energized can cause electrical damage or system faults.

• How does the PLC-5 processor exchange data tables with the BASIC module coprocessor?

  Data transfers between the PLC-5 processor and the 1771-DB module occur via Block Transfer Read (BTR) and Write (BTW) routines.

• What function does the internal coprocessor perform relative to the main PLC-5 CPU?

  It offloads BASIC program execution and ASCII string handling, running independently of the main controller scan cycle.

• How are serial cable shields grounded during field installation?

  Cable shield braids must be connected to a single-point chassis ground lug to prevent ground loops and noise injection.

• What operating temperature envelope applies to the 1771-DB hardware in an enclosure?

  The hardware operates within ambient cabinet temperatures ranging from 0 deg C up to 60 deg C without external cooling.

• How are communication protocols aligned with system firmware updates?

  Port settings and program memory interface through system firmware flash compatibility routines managed in user logic.