Allen-Bradley 1785-L46B PLC-5/46 Controller 48K

Allen‑Bradley 1785‑L46B PLC‑5/46 Processor – Enhanced Performance with Protected Memory

The Allen‑Bradley 1785‑L46B is a high‑capacity enhanced processor from the PLC‑5 family. This controller stands out with its integrated protected memory, which safeguards critical program blocks, routines, and I/O configurations from unauthorized modifications. It offers 48 kilowords of battery‑backed user memory, providing ample space for complex automation sequences. Additionally, the processor draws 3.0 A from the backplane at 5 V DC and dissipates approximately 17.3 W (59.04 BTU/hr) during normal operation. The 1785‑L46B is designed for large‑scale systems that demand both performance and security.

Memory Protection and Data Security

One of the most notable features of the 1785‑L46B is its integrated protected memory. Unlike standard processors, this controller restricts access to proprietary information such as program blocks, routines, and operational parameters. This protection extends to the controller operating mode and I/O configuration, ensuring that these critical settings are only modified when absolutely necessary. Therefore, the 1785‑L46B is an excellent choice for applications where intellectual property protection and process integrity are paramount. For program backup, you can install EEPROM modules like the 1785‑ME32, ‑ME64, or ‑M100 into the front panel slot.

Communication Capabilities

The 1785‑L46B comes equipped with four combo ports, each configurable for Data Highway Plus (DH+) or Remote I/O (RIO) protocol. These ports can operate in either Adapter or Scanner mode, giving you exceptional flexibility for network architecture. You can build extensive DH+ peer‑to‑peer networks or connect numerous remote I/O racks across your facility. Additionally, a 25‑pin D‑shell serial port supports RS‑232, RS‑422, and RS‑423 standards. This serial port primarily uses the DF1 protocol in full‑duplex or half‑duplex mode, making it compatible with programming terminals and HMIs. The control coprocessor expansion port is also available for advanced applications. Furthermore, voltage isolation exists between the communication ports and between the ports and the relay cartridge, tested at 500 V and 1000 V for 60 seconds. This isolation enhances reliability in electrically noisy industrial environments.

I/O Capacity and Chassis Support

The 1785‑L46B handles up to 2048 total I/O points in any mix of discrete and analog modules. Alternatively, you can configure complementary operation with 2048 inputs and 2048 outputs simultaneously. The analog I/O capacity also reaches 2048 points, making this controller suitable for process‑intensive applications. For addressing, the processor supports three modes: 2‑slot, 1‑slot, and ½‑slot addressing, accommodating various module densities including 8‑point, 16‑point, 32‑point, and intelligent Bulletin 1771, 1794, 1746, and 1791 I/O modules. In total, the 1785‑L46B manages up to 61 I/O chassis. Specifically, it supports up to 32 universal remote chassis per I/O link, while extended local chassis are not supported. The I/O scan time is 10 ms at 57.6 kbit/s, 7 ms at 115.2 kbit/s, and 3 ms at 230.4 kbit/s for remote racks. Program scan time is 0.5 ms per K word for bit logic and 2 ms per K word for typical operations.

Front Panel Indicators and Mode Selection

The front panel of the 1785‑L46B includes comprehensive status indicators. A BATT LED monitors battery condition, while a PROC LED shows the processor’s operating state. The FORCE LED indicates when I/O forces are active, and a COMM LED displays serial port activity. Each of the four communication ports also has dedicated status indicators. A three‑position keyswitch lets you select RUN, PROG, or REM modes. In RUN mode, the processor executes the program and activates outputs. PROG mode halts execution for programming and maintenance. REM mode enables remote programming while the controller continues its logic scan. This design provides clear visual feedback and simplified system management.

Real‑Time Clock and Timing Accuracy

The 1785‑L46B includes an internal real‑time clock with a variation of ±5 minutes per month at 60 °C. The timing accuracy is 1 program per scan, which supports time‑stamped data logging and scheduled operations. This feature is particularly valuable for batch processing, shift reporting, and event sequencing applications where precise timing is essential.

Power and Environmental Specifications

The 1785‑L46B requires a backplane current of 3.0 A at 5 V DC and dissipates 17.3 W of power. It operates within a temperature range of 0 °C to 60 °C (32 °F to 140 °F) with a relative humidity of 5‑95% without condensation. For storage, it withstands temperatures from ‑40 °C to 85 °C (‑40 °F to 185 °F). The processor can endure a 30G shock and a 1G vibration at 10‑500 Hz, making it robust for demanding industrial environments. It is designed for open‑enclosure installations and weighs 1.42 kg. The 1785‑L46B holds UL, CSA, C‑TICK, and CE certifications, ensuring global regulatory compliance.

Installation Guidelines

Install the 1785‑L46B in the left‑most slot of a 1771 chassis (models ‑A1B, ‑A2B, ‑A3B, ‑A3B1, or ‑A4B). Begin by turning off chassis power before inserting the processor. Align the module with the card guides and push it firmly into the backplane connector until it seats properly. Secure the module using the retaining screws. The processor is keyed to the chassis via connections between pins 40‑42 and 54‑56 of the backplane top connector. Next, connect DH+ or Remote I/O cables to the four combo ports as required. Attach serial devices to the 25‑pin D‑shell port for programming or HMI communication. Finally, set the keyswitch to the desired mode and apply power. Always verify that the total backplane current does not exceed your power supply rating.

Packaging List

• Allen‑Bradley 1785‑L46B PLC‑5/46 processor module (1 unit)

• 1770‑XYC battery (pre‑installed)

• Installation and quick start guide (printed)

• Serial port dust cover

Note: Cables, EEPROM modules, and relay cartridges are sold separately.

Shipping Information

We ship worldwide via FedEx, UPS, or DHL. Tracking numbers will be provided within 24 hours after dispatch.

Frequently Asked Questions

1. What makes the 1785‑L46B different from other PLC‑5 processors?
The 1785‑L46B features integrated protected memory, which restricts access to critical program data, routines, and I/O configurations. This adds a layer of security not found in standard models.

2. How many communication ports does the 1785‑L46B have?
This processor includes four combo ports configurable for DH+ or Remote I/O, plus one dedicated serial port for RS‑232/422/423 connections.

3. What is the maximum I/O capacity of the 1785‑L46B?
The 1785‑L46B supports up to 2048 I/O points in any mixed configuration, or 2048 inputs and 2048 outputs in complementary mode.

4. Does the 1785‑L46B support extended local I/O chassis?
No, this controller does not support extended local I/O chassis. However, it supports up to 32 universal remote chassis per I/O link and 61 total chassis.

5. What certifications does the 1785‑L46B hold?
The 1785‑L46B is certified with UL, CSA, C‑TICK, and CE, making it suitable for international industrial installations.