Allen-Bradley FLEX I/O Modules: 1794-ASB,

Technical Dossier

Product Details And Specifications

Allen-Bradley FLEX I/O Series Technical Notes

The Allen-Bradley FLEX I/O platform (1794 series) is a distributed I/O system developed by Rockwell Automation for integration with ControlLogix, CompactLogix, SLC 500, and PLC-5 controllers. Deployed across global heavy industry — including petrochemical refineries, nuclear power auxiliary systems, offshore platforms, and continuous-process chemical plants — the 1794 series provides modular, rack-based I/O expansion over standard industrial networks including DeviceNet, ControlNet, EtherNet/IP, and Remote I/O. Its compact form factor and broad protocol support have made it a long-cycle asset in facilities where control system replacement is constrained by capital expenditure cycles of 15–25 years.

The Evolution of FLEX I/O Architecture

The 1794 FLEX I/O platform was introduced in the mid-1990s as a response to demand for distributed I/O that could operate over existing plant cabling infrastructure. The initial release supported Remote I/O (RIO) and DH-485 networks, targeting SLC 500 and PLC-5 installations. Subsequent adapter revisions added ControlNet (1794-ACN, 1794-ACNR) and DeviceNet (1794-ADN) support, enabling integration with ControlLogix architectures introduced in 1997.

The EtherNet/IP adapter (1794-AENT) was introduced in the early 2000s, aligning the platform with Ethernet-based plant networks and CIP (Common Industrial Protocol) communication. This revision remains the most widely deployed adapter variant in active installations. The 1794-AENTR added redundant media capability for fault-tolerant topologies.

As of 2024, Rockwell Automation has announced end-of-life timelines for several 1794 adapter and I/O modules. Facilities operating legacy RIO-based adapters (1794-ASB, 1794-ASB/B) face the most immediate obsolescence risk. Migration paths include the 1734 POINT I/O platform and 5069 Compact I/O for new installations, though direct hardware replacement is not always feasible in existing panel configurations.

FLEX I/O Full Catalog & Functionalities (SKU List)

Remote I/O / Serial Adapters

• 1794-ASB: Remote I/O adapter, full-rack addressing, SLC/PLC-5 compatible
• 1794-ASB/B: Revised Remote I/O adapter, enhanced noise immunity revision B
• 1794-ASB2: Remote I/O adapter, half-rack addressing mode support

Network Adapters

• 1794-ACN15: ControlNet adapter, coax media, 1.5 Mbps, single port
• 1794-ACNR15: ControlNet adapter, redundant coax media, fault-tolerant ring
• 1794-ADN: DeviceNet adapter, Group 2 slave, 125/250/500 kbps
• 1794-AENT: EtherNet/IP adapter, single port, 10/100 Mbps, CIP messaging
• 1794-AENTR: EtherNet/IP adapter, dual port, DLR (Device Level Ring) topology

Digital Input Modules

• 1794-IB16: 16-point 24VDC digital input, sink/source compatible
• 1794-IB32: 32-point 24VDC digital input, high-density rack
• 1794-IA16: 16-point 120VAC digital input module
• 1794-IV16: 16-point TTL/5VDC digital input, encoder interface capable

Digital Output Modules

• 1794-OB16: 16-point 24VDC digital output, 0.5A per point, source type
• 1794-OB32: 32-point 24VDC digital output, high-density
• 1794-OA16: 16-point 120/240VAC digital output, triac isolated

Analog I/O Modules

• 1794-IE8: 8-channel analog input, 4–20mA / 0–10V, 12-bit resolution
• 1794-OE4: 4-channel analog output, 4–20mA / 0–10V, 12-bit resolution
• 1794-IE4XOE2: Combination 4AI / 2AO analog module, mixed signal
• 1794-IT8: 8-channel thermocouple input, J/K/T/E/R/S/B types supported
• 1794-IR8: 8-channel RTD input, PT100/PT1000/Ni/Cu sensor types

Power Supply / Terminal Base

• 1794-TB3: 3-wire terminal base, screw-type, standard I/O module mounting
• 1794-TB3S: 3-wire terminal base with spring-clamp termination
• 1794-TBN: Terminal base, standard, for network adapter modules
• 1794-PS13: 24VDC power supply, 1.3A output, DIN rail mount

Sourcing Hard-to-Find & Obsolete FLEX I/O Parts

For facilities operating SLC 500 or PLC-5 systems with existing 1794-ASB adapters, full controller migration is frequently not economically viable within a single maintenance cycle. DriveKNMS provides tested, serialized replacement units with documented firmware revision levels to ensure backward compatibility with installed base configurations. All units are cross-referenced against Rockwell Automation's product lifecycle database prior to shipment.

Quality Control for the FLEX I/O Range

Each 1794 series module processed by DriveKNMS undergoes a structured verification protocol prior to dispatch. Adapter modules (1794-ASB, 1794-AENT, 1794-ADN) are bench-tested for backplane communication integrity using a live 1794 rack assembly with known-good I/O modules. Network communication is verified at the protocol layer: RIO adapters are tested for correct rack address response and data table mapping; EtherNet/IP adapters are verified for CIP connection establishment and I/O data exchange.