Allen-Bradley 1785-L26B PLC-5/26 Processor – 16K SRAM

June 11, 2026 • 2 min read • wayne • Science

Summary

The Allen-Bradley 1785-L26B is a robust PLC-5/26 standard processor with 16 Kilowords of battery-backed SRAM. It controls up to 512 I/O points in any mix, supports multiple remote chassis, and operates in harsh industrial environments from 0 to 60°C.

Expert Technical Evaluation & Performance Review

Memory and I/O Architecture

The 1785-L26B uses protected memory to safeguard critical logic from unauthorized changes. Its 16 Kilowords SRAM retains data through battery backup, ensuring uptime. Engineers can expand I/O to 512 analog points or a complementary 512 inputs plus 512 outputs.

Communication and Network Integration

This controller integrates one RS-232/422/423 serial port and a DH+ port for Data Highway Plus networking. A remote I/O port (Channel 1B) connects distant devices. The I/O scan time adjusts from 10 ms at 57.6 kbit/s down to 3 ms at 230.4 kbit/s, enabling fast data exchange.

Environmental Durability

The unit withstands 30G shock and 1G vibration at 10-500 Hz. It runs reliably at 0 to 60°C with 5-95% non-condensing humidity. UL, CE, CSA, and C‑TICK certifications confirm compliance with global safety standards.

Backplane Power and Isolation

It draws a maximum of 2.6 amps at 5 V DC from the 1771 chassis. Voltage isolation between communication ports is tested at 500 V for one minute; between port and relay cartridge at 1000 V for one minute, safeguarding against surges.

Addressing and Module Support

Three hardware addressing modes (half-slot, 1-slot, 2-slot) allow mixing 8‑, 16‑, and 32‑point modules. The controller supports 1771, 1794, 1746, and 1791 I/O modules, plus the 1785-RC relay cartridge for external device interface.

Buyer's Guide: Key Considerations

Procurement managers should verify that the 1785-L26B fits the left-most slot of a 1771 chassis. It supports up to 13 I/O chassis total, with 12 universal remote units. Ensure your power supply can deliver 2.6 A at 5 V DC. The open‑style enclosure weighs 1.42 kg and is suitable for cabinet mounting.