Overview
Allen-Bradley 1785-L40B is a PLC-5/40 standard processor module from the legacy PLC-5 family, designed for medium to large-scale industrial automation systems. The unit features 40K memory capacity and is designed for installation in a 1771 I/O chassis. This controller offers 48K words of user memory and supports 2048 (any mix) I/O or 2048 in + 2048 out (complementary). The 1785-L40B is ideal for retrofit and legacy system upgrades where PLC-5 platform continuity is required.
Key Features
- Embedded communication with Four (4) DH+/Remote I/O (Adapter or Scanner) and one (1) serial port configurable for RS-232, 423, and RS-422A standards.
- Battery-backed static RAM protects program and data in case of power loss.
- Four DH+ port mode and universal remote I/O (adapter or scanner) with a maximum of 32 I/O chassis per I/O link.
- EEPROM removable program backup for data retention and program portability.
- Mounts to PLC-5 chassis such as 1771-A1B, 1771-A2B, 1771-A3B, 1771-A3B1, and 1771-A4B.
Technical Specifications
- User Memory: 48K words (battery-backed SRAM)
- Max I/O Capacity: 2048 analog and discrete I/O (combined or separate)
- Communication Ports: 4 DH+/Remote I/O channels; 1 serial port (RS-232/422/423)
- Backplane Current: 3.3A at 5VDC
- Power Dissipation: 17.3 Watts
- Max I/O Chassis (Universal Remote): 32 max per I/O link
- Series: PLC-5 legacy platform
- Program Backup: EEPROM (removable)
Typical Applications
This controller is ideally used for medium to large automation applications built with 48K words user memory capable of handling any combination of I/O devices. Common uses include discrete manufacturing, bottling and packaging, automotive assembly, chemical processing, and facility automation where legacy PLC-5 infrastructure remains operational.
Compatibility & Replacements
Compatible With
- 1771 series I/O chassis (1771-A1B, 1771-A2B, 1771-A3B, 1771-A3B1, 1771-A4B)
- 1771 discrete, analog, and specialty I/O modules
- 1785-ME memory expansion modules (1785-ME16, 1785-ME32, 1785-ME64, 1785-ME100)
- DH+ network and Remote I/O (RI) communication architecture
- RS-232/422/423 serial devices and gateways
Replaces / Drop-In Replacement For
- Earlier 1785-L40 Series A/B/C revisions (verify firmware compatibility)
- Field upgrades from 1785-L30B (higher memory alternative available)
- Verify compatibility with your system integrator before ordering.
Works With
- PLC-5 ladder logic programming environment (offline and online editing)
- DH+ and Remote I/O communication protocols
- Allen-Bradley software: RSLogix 5, PC VistaPro
- Third-party SCADA and HMI packages supporting RS-232/422 communication
- Legacy industrial Ethernet bridges (via serial gateway modules)
