Allen-Bradley 1769-ASCII CompactLogix Interface Module

The Allen-Bradley 1769-ASCII, also cataloged as the 1769-ASCII Communication Module, operates as a dedicated hardware component for serial ASCII protocol execution within CompactLogix platforms.

Hardware Specifications

Backplane Bus Communication and Serial Network Expansion

Engineers integrate the 1769-ASCII module into CompactLogix or MicroLogix 1500 system racks to bridge serial devices with controller logic over the backplane bus. The module processes full-duplex RS-232/RS-422 and half-duplex RS-485 protocols across two independently configurable channels, which prevents data bottlenecks during simultaneous transmit and receive cycles. Furthermore, onboard buffer management handles TX/RX FIFO queues to mitigate overflow errors, while continuous 30 V isolation protects controller backplane logic from ground loops and field-side electrical noise.

Frequently Asked Questions

Q: How does backplane current draw limit the placement of the 1769-ASCII module?

A: The module draws 425 mA at 5 VDC directly from the CompactLogix backplane, requiring installation within a power supply distance rating of four modules to maintain bus rail stability.

Q: How do technicians verify communication status and diagnose channel framing errors?

A: Diagnostic status bits report TX/RX FIFO overflows, parity errors, and handshake faults directly to controller tags, while LED indicators provide visual feedback for active port activity.

Field Installation Guidelines

Technicians must verify that main system rack power remains off before inserting or removing the 1769-ASCII module. Align the module tongue-and-groove slots with the adjacent Compact I/O module, sliding the unit until the backplane bus connectors interlock completely. Secure the panel-mounting feet or DIN-rail latch to establish chassis ground continuity through the mounting assembly.

Route serial communications wiring using Belden 8761 shielded cable, keeping signal conductors separated from high-voltage AC lines inside cabinet wire ducts. Connect cable shields directly to dedicated earth ground points to suppress electromagnetic interference, and ensure field cables do not exceed maximum RS-232 or RS-485 length specifications. Maintain adequate ventilation clearance around module cooling vents to ensure continuous convective heat dissipation.