Allen-Bradley 1771 Modules: 1771-IVN/C

Technical Dossier

Product Details And Specifications

Allen-Bradley 1771 Series Technical Notes

The Allen-Bradley 1771 I/O system is one of the most widely deployed programmable controller I/O platforms in global heavy industry. Installed across petrochemical refineries, nuclear power generation facilities, offshore platforms, pulp and paper mills, and continuous process chemical plants, the 1771 backplane architecture has served as the field I/O backbone for PLC-5 processors since the early 1980s. Its modular slot-based design — supporting up to 16 I/O slots per chassis — enabled scalable, distributed control architectures that remain operational in thousands of facilities worldwide. The 1771-IVN/C is a 32-point, 24VDC DC input module designed for high-density digital signal acquisition within this platform.

The Evolution of 1771 Architecture

The 1771 I/O platform was introduced by Allen-Bradley (now Rockwell Automation) in the early 1980s as the standard I/O subsystem for the PLC-5 processor family. The architecture uses a parallel backplane bus operating at TTL logic levels, with each module occupying one or two I/O slots in a 1771-Axx chassis. Early revisions (Series A/B) established the physical form factor and backplane pinout that remained consistent through subsequent series revisions, ensuring backward compatibility across decades of production.

Through the 1990s, the platform expanded to include analog, specialty, and communication adapter modules. The introduction of the 1771-ACN15 and 1771-ACNR ControlNet adapters extended the platform into networked I/O architectures. By the 2000s, Rockwell Automation had designated the PLC-5 and 1771 I/O as mature products, with end-of-life announcements issued progressively through the 2010s. As of 2024, the 1771 I/O series is fully discontinued, with no new production. Facilities running PLC-5 systems must source replacement modules from authorized aftermarket suppliers or execute migration to the ControlLogix / 1756 platform.

Compatibility note: 1771 modules are chassis-specific. The 1771-A1B (4-slot), 1771-A2B (8-slot), 1771-A3B1 (12-slot), and 1771-A4B (16-slot) chassis are the primary enclosures. Module series revisions (A, B, C, D) are generally backward-compatible within the same module family but must be verified against the specific PLC-5 processor firmware revision.

1771 Full Catalog & Functionalities (SKU List)

Digital Input Modules (DI)

• 1771-IVN/C: 32-point, 24VDC DC input module, high-density field signal acquisition for PLC-5 systems.
• 1771-IAD: 16-point, 120VAC input module, standard AC field device interfacing.
• 1771-IBD: 16-point, 24VDC input module, standard density DC digital input.
• 1771-ICD: 16-point, 48VDC input module, medium-voltage DC input applications.
• 1771-IGD: 16-point, 125VDC input module, high-voltage DC input for substation environments.
• 1771-IND: 32-point, 24VDC input module, high-density DC input, predecessor to IVN series.
• 1771-IX: 8-point, TTL-level input module, logic-level signal acquisition from solid-state sensors.

Digital Output Modules (DO)

• 1771-OAD: 16-point, 120VAC output module, standard AC load switching.
• 1771-OBD: 16-point, 24VDC output module, standard density DC digital output.
• 1771-ODD: 16-point, 24VDC isolated output module, noise-sensitive environment applications.
• 1771-OND: 32-point, 24VDC output module, high-density DC output.
• 1771-OVN: 32-point, 24VDC output module, high-density DC output, paired counterpart to 1771-IVN/C.
• 1771-OW16: 16-point relay output module, dry contact switching for mixed-voltage field loads.

Analog Modules (AI/AO)

• 1771-IFE: 8-channel analog input, 4–20mA / 0–10V, 12-bit resolution.
• 1771-IFE/B: Enhanced 8-channel analog input, improved noise immunity over base IFE revision.
• 1771-OFE1: 4-channel analog output, 4–20mA, 12-bit resolution, process loop control.
• 1771-OFE2: 4-channel analog output, 0–10V, 12-bit resolution, voltage-mode process output.

Communication & Adapter Modules

• 1771-ACN15: ControlNet I/O adapter, 1.5Mbps, connects 1771 chassis to ControlNet network.
• 1771-ACNR15: Redundant ControlNet I/O adapter, dual-port, fault-tolerant network topologies.
• 1771-ASB: Remote I/O adapter, connects 1771 chassis to PLC-5 Remote I/O (RIO) network.
• 1771-DCM: Data communication module, DH+ network interface for 1771 chassis.

Power Supply Modules

• 1771-P4S: 5VDC, 4A chassis power supply, standard 1771 backplane power.
• 1771-P7: 5VDC, 10A chassis power supply, high-current supply for fully populated chassis.

Sourcing Hard-to-Find & Obsolete 1771 Parts

For obsolete modules with no direct replacement, DriveKNMS can advise on third-party retrofit solutions and I/O conversion interfaces that allow 1771 field wiring to be reused with modern ControlLogix or CompactLogix I/O systems, reducing rewiring costs during migration projects.

Quality Control for the 1771 Range

The 1771 backplane uses a parallel TTL bus architecture with module-specific address decoding. Quality verification for 1771 modules requires chassis-level functional testing rather than standalone bench testing, as module health is only fully validated under active backplane communication with a PLC-5 processor.