The Allen-Bradley 1771-ASB is a critical component for any PLC-5 system. This Universal Remote I/O Adapter Module serves as the primary interface between your controller and distributed I/O modules. Its purpose is to drastically reduce wiring costs and simplify system layout. By placing I/O closer to actual sensors and actuators, you save on installation and maintenance. The module operates with a backplane current of 1.0 Amps at 5 Volts DC. It supports a broad range of communication rates, including 57.6 Kbps, 115 Kbps, and 230 Kbps. This flexibility allows you to optimize speed against distance for your specific plant floor. It weighs just 1.9 pounds and fits into a standard 1771 I/O chassis.
Step-by-Step Installation Guide for the 1771-ASB
You must install this module in the left-most slot of the 1771 chassis. This specific position is required for proper backplane communication. The chassis can support 4, 8, 12, 16, or 32 total slots. The module then controls all I/O modules located to its right. For wiring, you must use a Belden 9463 cable, often called "Blue Hose." This cable is the industry standard for Remote I/O protocol. Attach the field wiring arm, specifically the 1771-WB connector, for secure connections. The lower connector keying is set between positions 16 and 18.
You must install a terminating resistor at both ends of the network. The daisy-chain topology requires these resistors to close the communication segment. For older RIO network configurations, use a 150 Ohm resistor. For enhanced RIO network versions, switch to an 82 Ohm resistor. The module supports up to 32 I/O adapter devices on the same link. You can select 1-slot or 2-slot I/O addressing for your chassis. The module improves scan time by automatically skipping the last four slots. This saves valuable I/O image space and speeds up your control loop.
The 1771-ASB provides three diagnostic indicators for quick troubleshooting. The ACTIVE LED must be solid green to indicate normal operation. The ADAPTER FAULT LED signals a problem with the module itself. The I/O RACK FAULT LED points to issues with the connected chassis. These LEDs help you identify problems instantly without special tools. The module reads and writes data in parallel form through the backplane. It supports serial communication over the RIO link for data transmission. The maximum cable length reaches 10,000 feet at 57.6K baud. For higher speeds, the distance reduces to 2500 feet at 230.4K baud. This gives you great flexibility for both local and remote installation.
Expert FAQ for the 1771-ASB
Which terminating resistor should I use for my RIO network?
You should use a 150 Ohm resistor for older configurations. Switch to an 82 Ohm resistor for enhanced RIO network versions.
How many I/O connections can this single adapter support?
This single adapter supports up to 32 I/O-adapter devices over the I/O link.
What is the maximum cable distance for this module?
The maximum cable distance is 10,000 feet at 57.6K baud. The distance drops to 2500 feet at 230.4K baud.
What does the ACTIVE LED color indicate for this module?
A solid green ACTIVE LED indicates the module is operating normally. Any other color means there is a problem.
Can I use this module in a hazardous location?
Yes, the module is certified for Class I, Division 2 Groups A, B, C, D. It also holds UL, CSA, and CE certifications.
Logistics & Standard Packaging Details
