Allen-Bradley 1746-BAS​ SLC 500 BASIC Language Module with 24KB RAM, RS-232/422/485 & DH-485 Ports for Custom Logic & ASCII Comms

Product Overview

The Allen-Bradley 1746-BAS​ is a single-slot programmable BASIC language module designed for the Rockwell Automation SLC 500 modular PLC chassis. It functions as an intelligent coprocessor that executes user-written programs in Intel BASIC-52 (MCS® BASIC-52 compatible) independently of the SLC 500 processor scan, providing advanced mathematical computation, floating-point arithmetic, string manipulation, data logging, and asynchronous serial communications that the standard SLC 500 instruction set cannot natively perform. The 1746-BAS​ occupies one I/O slot in a 1746 chassis and interfaces with the SLC processor through mapped input/output image registers, allowing bidirectional data exchange between the BASIC program and the ladder logic application running in the main CPU (such as a 1747-L551 or 1747-L532).Equipped with 24 KB of battery-backed static RAM for user program and data storage, two isolated serial communication ports (configurable for RS-232C, RS-422, or RS-485), and one DH-485 network port (RJ-45), the Allen-Bradley 1746-BAS​ is ideally positioned to serve as a protocol bridge, operator interface driver, barcode reader/printer controller, or custom data acquisition node within legacy and retrofit automation systems. It supports baud rates up to 19.2 kbps on the serial ports and includes a built-in real-time clock/calendar for time-stamped data logging. An optional 1747-M13 (8 KB) or 1747-M15 (32 KB) EEPROM memory module can be plugged into the front socket for non-volatile program retention independent of the backup battery.Because the 1746-BAS​ runs its BASIC program asynchronously in a background multitasking fashion, it offloads complex string parsing (such as NMEA, ASCII weight values, or barcode data), floating-point calculations, and custom serial protocol emulation from the SLC processor—extending the useful life and capability of installed SLC 500 systems in applications where upgrading to a newer ControlLogix or CompactLogix platform is not yet justified. The module is particularly valued in industries maintaining legacy SLC 500 infrastructure for its ability to interface third-party ASCII devices, implement custom operator messages on serial displays, and perform math-intensive routines such as statistical process control (SPC) calculations.

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Description

 

Technical Specifications

Product Model | 1746-BASManufacturer | Allen-Bradley / Rockwell AutomationProduct Type | SLC 500 Programmable BASIC Language Module (Coprocessor)User Program/Data Memory | 24 KB Battery-Backed SRAM (retained by 1747-BA lithium battery)Optional EEPROM Expansion | Supports 1747-M13 (8 KB) or 1747-M15 (32 KB) non-volatile memory cartridgeProgramming Language | Intel BASIC-52 (MCS BASIC-52 compatible), supports floating point & string opsSerial Ports | 2 × Isolated Programmable Asynchronous Ports (Port 1 & Port 2): RS-232C, RS-422, RS-485 (software selectable); up to 19.2 kbpsDH-485 Port | 1 × RJ-45 DH-485 port for connection to SLC 500 processor or panel (peer-to-peer messaging)Real-Time Clock | Built-in RTC with battery backup (YY/MM/DD HH:MM:SS)Backplane Current Draw | 150 mA @ 5 V DC; 40 mA @ 24 V DC (typical)I/O Image Exchange | Up to 64 Input Words + 64 Output Words mapped through SLC processor I/O scanIndicators | MODULE OK (Green/Red), RUN (Green), BATTERY LOW (Yellow/Amber), PORT 1 / PORT 2 ActivityBattery Type | 1747-BA (3 V Lithium, CR14250 style, also shared with SLC 500 CPUs)Slot Width | 1 Slot (Standard SLC 500 Module Width: 35 mm / 1.38 in)Operating Temperature | 0 °C to +60 °C (32 °F to 140 °F)Dimensions (H×W×D) | 141 × 35 × 132 mm (5.55 × 1.38 × 5.20 in)Certifications | cULus Listed, CE Marked, C-Tick

Main Features and Advantages

Embedded BASIC-52 coprocessing for offloaded computation: The 1746-BAS​ executes user BASIC programs independently of the SLC 500 scan cycle, making it possible to perform floating-point math, statistical calculations (mean, standard deviation for SPC), trigonometric functions, and complex string parsing—capabilities absent from native SLC 500 ladder instructions. Data is exchanged seamlessly through SLC I/O image tables, letting the main processor read computed results or send raw data to the BASIC module every scan.Dual isolated serial ports with multi-protocol flexibility: Both PRT1 and PRT2 on the 1746-BAS​ are software-configurable for RS-232, RS-422, or RS-485 electrical interfaces and support user-defined handshaking (XON/XOFF, hardware RTS/CTS). This allows simultaneous connection to an ASCII barcode scanner on one port and a serial printer or modem on the other, or implementation of a custom master polling routine to a third-party device using a non-standard ASCII protocol—effectively functioning as a low-cost protocol gateway within the SLC 500 rack.DH-485 peer networking: The dedicated DH-485 RJ-45 port enables the 1746-BAS​ to communicate directly with the SLC 500 processor, PanelView terminals, or other DH-485 nodes for messaging, status reporting, or uploading/downloading the BASIC program using Rockwell’s programming software (RSLogix 500 / APS). This eliminates the need for an external serial converter when configuring or monitoring the module from an engineering workstation connected to the DH-485 network.Non-volatile program options & battery-backed RAM: The 24 KB SRAM retains the user BASIC program and variables as long as the 1747-BA backup battery is good (typical life 2–5 years depending on ambient temperature). For permanent storage unaffected by battery failure, programs can be saved to an optional EEPROM cartridge (1747-M13/M15) and auto-loaded on power-up—a critical feature for unattended machines where a dead battery must not cause loss of the custom application logic.Real-time clock and data logging: With its onboard RTC, the 1746-BAS​ can time-stamp events, log process data to a serial printer in CSV format, or schedule timed actions. This is especially useful in batch traceability, downtime recording, and audit-trail applications in food, pharma, and regulated industries still running SLC 500 platforms.Expandable and hot-swappable within limits: The module can be inserted or removed from a powered chassis (with the SLC processor in Program mode or appropriate fault handling programmed) when using a removable-style chassis, and the front-panel LEDs give immediate visual diagnosis of run status, battery condition, and serial port activity—reducing troubleshooting time during commissioning and maintenance.

Application Field

The Allen-Bradley 1746-BAS​ is most commonly deployed in legacy SLC 500-based systems that require interfacing with non-Rockwell ASCII devices such as barcode scanners, weigh scales with serial output, inkjet printers, vision system cameras, or third-party variable frequency drives that accept ASCII command strings. In a typical packaging line retrofit, the 1746-BAS​ reads weight values from a serial-checkweigher in real time, parses the ASCII string, performs tare and statistical analysis in BASIC, and writes the computed accept/reject decision back to the SLC 500 processor’s integer file—all without burdening the main PLC scan or requiring an expensive protocol gateway.Another prevalent use case is data logging and report generation: the 1746-BAS​ can periodically poll process variables from the SLC processor via mapped I/O words, format them with date/time stamps, and send formatted lines to a serial line printer or a connected PC running a terminal emulator—providing a low-cost batch record or shift report directly from the control rack. In water/wastewater and bulk-material handling plants, the module has been used to implement custom ASCII master protocols to legacy analyzers or to convert DH-485 messages into plain-text SMS alerts via an attached GSM modem on one of its serial ports.Machine builders and OEMs with long-running SLC 500 installations also leverage the 1746-BAS​ to drive character-based serial operator displays (LCD or vacuum-fluorescent) showing custom messages, setpoints, or diagnostic text that would be impractical to generate through the SLC ladder alone. Because the module’s BASIC program is stored locally and executes autonomously (once initialized by the SLC processor), it continues to handle serial I/O and string operations even if the main processor is temporarily in Program mode—provided backplane power remains present. This characteristic makes the 1746-BAS​ a uniquely flexible legacy-expansion tool for extending the functional life of SLC 500 control systems in industries ranging from food & beverage and plastics to metals and utilities.

Contact Us WhatsApp / Wechat：+86 18150087953
Phone：+86 18150087953
Email：sales@cxplcmro.com

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