Allen-Bradley 1771-ASB PLC-5 Remote I/O Adapter Module

Description

Product Introduction

The Allen-Bradley 1771-ASB is a Universal Remote I/O (RIO) adapter module engineered for 1771 I/O chassis platforms. Placed in the far-left slot of a 1771 chassis, it acts as the communication link between local discrete and analog I/O modules and a remote master processor (such as a PLC-5, SLC 5/02 through 5/05 with RIO scanner, or ControlLogix 1756-RIO scanner).

Utilizing Allen-Bradley’s classic twinaxial “Blue Hose” cable architecture, the 1771-ASB converts backplane I/O signals into deterministic serial RIO network traffic. Supporting baud rates up to 230.4 Kbps and flexible rack-addressing options, it allows legacy plant architectures to extend I/O drops thousands of feet across harsh manufacturing environments without moving main CPU hardware.

Key Technical Specifications

Application Scenarios & The “Trench” Experience

The Trench Story

It is 2:00 AM in an aging paper mill. A 1771-A3B chassis housing critical 120VAC solenoids loses all communication to the main PLC-5 processor over a long twinax blue-hose run. The adapter status LED flashes red, indicating an internal firmware/communication failure on the legacy 1771-ASB adapter. Modernizing the entire 16-slot 1771 rack to ControlLogix Ethernet during a night shift is out of the question. Dropping in a tested replacement 1771-ASB module, matching the 8-position DIP switch banks (SW1 and SW2) to set the exact rack address and baud rate, and snapping the 1771-P4 arm back into place restores remote I/O scanning in less than fifteen minutes.

Specific Applications

• Remote Motor Control Centers (MCCs): Transmits discrete start/stop commands and run status from remote electrical rooms to central control rooms.
• Legacy Automotive Stamping Line Upgrades: Connects existing 1771 I/O chassis drops to modern ControlLogix PACs using 1756-RIO scanner modules.
• Chemical Batching Tanks: Routes analog temperature and pressure values from field-mounted 1771-IFE cards back to a central PLC-5 controller over shielded blue hose.
• Large Water Treatment Facilities: Spans long physical distances between filter galleries and main PLC control panels using 57.6 Kbps low-speed RIO runs.

1771-ASB

1771-ASB

1771-ASB

Transparency SOP: Quality Assurance & Testing

Every 1771-ASB adapter module undergoes rigorous hardware and network bench testing prior to shipment:

1. Physical & Card-Edge Inspection: We clean and inspect backplane gold card-edge fingers, check enclosure side plastic guide rails, and verify that DIP switches move smoothly with clean contact latching.
2. Backplane & Power Test: The module is installed into a 1771-A2B chassis with a 1771-P7 power supply to confirm logic power distribution and backplane rail health.
3. Active RIO Network Polling Test: We connect the adapter to an active Remote I/O scanner (PLC-5/40 or 1756-RIO) over Belden 9463 cable, cycling through 57.6k, 115.2k, and 230.4k baud configurations.
4. I/O Block Transfer Verification: The module is tested with high-density discrete cards and analog 1771-IFE/OFE modules to verify that block transfers (BTR/BTW) execute without checksum errors.
5. DIP Switch Register Audit: We verify that every DIP switch position accurately alters rack size, starting slot, baud rate, and hold-last-state behavior in controller registers.

The Veteran’s Tech Trap Guide

• ⚠️ Match DIP Switches SW1 & SW2 Before Power-Up: The 1771-ASB reads its hardware DIP switches (SW1 and SW2 on the board) ONLY during power-up. Changing DIP switch positions while power is applied will have no effect until you cycle 120VAC power to the 1771 chassis supply.
• ❗ Mind the 82-Ohm / 150-Ohm Termination Resistors: A Universal RIO network line MUST have termination resistors installed across the line ends (terminals 1 and 2 on the 1771-P4 arm). Use 150 \Omega resistors for 57.6k and 115.2k baud, or 82 \Omega resistors for 230.4k baud runs. Missing termination resistors cause signal reflections and intermittent “Rack Fault” indicators.
• ⚠️ Pay Attention to Series Differences (Series A/B vs. Series E): Newer series (like Series E and N) support expanded features such as 230.4k baud rates and extended block transfers. If you are replacing a Series E unit, using an older Series A or B unit might cause block transfer timing failures on newer analog cards.
• ❗ Do Not Connect 120VAC Power to the Blue Hose Terminal: The 1771-P4 field wiring arm on the 1771-ASB is strictly for low-voltage signal wiring (Blue, Shield, Clear). Accidentally landing 120VAC supply wires on the adapter terminal block will instantly destroy the serial transceiver ICs.

Frequently Asked Questions

Q: What is the maximum distance a 1771-ASB can be located from the main processor?

Maximum distance depends on the configured baud rate over Belden 9463 cable:

• 57.6 Kbps: Up to 10,000 feet (3,048 meters)
• 115.2 Kbps: Up to 5,000 feet (1,524 meters)
• 230.4 Kbps: Up to 2,500 feet (762 meters)

Q: What do the status LEDs on the front panel of the 1771-ASB indicate?

• ACTIVE (Green): Module is powered and actively communicating with the RIO scanner.
• ADAPTER FAULT (Red): Internal module self-test failure or hardware fault.
• I/O RACK FAULT (Red): Communication loss on the RIO link or backplane communication error with a chassis module.

Q: What wiring terminal block is used with the 1771-ASB?

The 1771-ASB uses the 1771-P4 field wiring arm, which plugs directly into the front connector of the adapter module.

Q: Can I control a 1771-ASB chassis using a modern ControlLogix PAC?

Yes. You can control 1771-ASB drops from a ControlLogix chassis using a 1756-RIO scanner module or via phased migration adapters (such as ProSoft Technology AN-X2-AB-DHRIO gateways).

Q: What is the difference between the 1771-ASB and the older 1771-AS adapter?

The 1771-AS is an older, legacy adapter limited to basic 57.6k baud rates and fewer rack addressing modes. The 1771-ASB is the upgraded Universal Remote I/O adapter supporting higher baud rates (up to 230.4k), block transfers, and flexible rack configurations (1/2-rack, 1/4-rack addressing).

Q: What warranty comes with your surplus or refurbished 1771-ASB modules?

Every 1771-ASB adapter module we supply includes our comprehensive 12-month replacement warranty. If a hardware fault occurs under normal operating conditions within 365 days of purchase, we replace the unit immediately from stock or issue a full refund.