The MicroLogix 1400 is a small Allen-Bradley controller that Rockwell still offers and that you will still find on packaged equipment in US plants. This guide covers what it is, how its file-based addressing works, which software programs it, its lifecycle status, and your options when it is time to migrate.
Independent resource. Not affiliated with or endorsed by Rockwell Automation. Specifications from Rockwell publications 1766-PP001D and 1766-RM001J, accessed September 28, 2026.
The Allen-Bradley MicroLogix 1400 (Bulletin 1766) is a small, fixed-I/O programmable logic controller from Rockwell Automation. Rockwell describes it as combining the MicroLogix 1100’s EtherNet/IP, online editing and built-in LCD with higher I/O count, faster high-speed counters and pulse-train output, and enhanced networking. It is the MicroLogix model Rockwell still offers now that the MicroLogix 1100 and 1200 are discontinued.
Key specifications from Rockwell’s product description (1766-PP001D):
Rockwell positions it for applications such as material handling, packaging, food and beverage, and water and wastewater. Its DNP3 and Modbus support suit remote telemetry and SCADA links. The built-in LCD lets a technician view controller and I/O status and read or write bit, integer and long values in the data table without a laptop.
The last letters of the catalog number encode power and I/O type. A trailing extra “A” means embedded analog I/O. Check the nameplate before you order a spare. An AWA and a BWA are not interchangeable, because their inputs are 120 V AC and 24 V DC respectively.
| Catalog number | Input power | Digital inputs | Digital outputs | Notable features |
|---|---|---|---|---|
| 1766-L32BWA | 120/240 V AC | 12 fast 24 V DC + 8 normal 24 V DC | 12 relay | Up to 6 high-speed counters at 100 kHz |
| 1766-L32AWA | 120/240 V AC | 20 × 120 V AC | 12 relay | No high-speed counter inputs |
| 1766-L32BXB | 24 V DC | 12 fast 24 V DC + 8 normal 24 V DC | 6 relay, 3 fast DC, 3 normal DC | High-speed counters, plus 3-channel PTO (100 kHz) / PWM (40 kHz) |
| 1766-L32BWAA | 120/240 V AC | 12 fast 24 V DC + 8 normal 24 V DC | 12 relay | Adds 4 voltage analog inputs and 2 voltage analog outputs |
| 1766-L32AWAA | 120/240 V AC | 20 × 120 V AC | 12 relay | Adds 4 voltage analog inputs and 2 voltage analog outputs |
| 1766-L32BXBA | 24 V DC | 12 fast 24 V DC + 8 normal 24 V DC | 6 relay, 3 fast DC, 3 normal DC | Analog I/O, high-speed counters and PTO/PWM |
Source: Rockwell Automation publication 1766-PP001D-EN-P, product specifications table. Accessed September 28, 2026.
The MicroLogix 1400 is a file-based controller. User memory is divided into program files, data files and function files. There are no free-form tags as in Studio 5000. Every value has an address made of a file type, a file number, an element and sometimes a word or bit. Once you can read these addresses, any RSLogix 500 program becomes readable.
Program files. Files 0 and 1 are reserved for the system. File 2 is the main ladder program that runs every scan, and files 3 to 255 are subroutines called with JSR. Interrupt routines are also subroutine files, pointed to by function files.
Data files. Files 0 to 8 have fixed default types that cannot be changed. You can add files 9 to 255 as bit, timer, counter, control, integer, floating point, string, ASCII, long word, message, PID or programmable limit switch files. Rockwell’s reference manual lists the controller at 20K of memory shared between program and data, with a maximum of 10K words of data.
| Data file | Identifier | File number (default first) | Words per element | Used for |
|---|---|---|---|---|
| Output | O | 0 | 1 | Values written to physical outputs during the output scan |
| Input | I | 1 | 1 | Values read from physical inputs during the input scan |
| Status | S | 2 | 1 | Controller status, fault bits, scan time and other system data |
| Bit | B | 3, 9–255 | 1 | General-purpose bits for internal logic |
| Timer | T | 4, 9–255 | 3 | Timer control word, preset and accumulator |
| Counter | C | 5, 9–255 | 3 | Counter control word, preset and accumulator |
| Control | R | 6, 9–255 | 3 | Length and position data for file, shift and sequencer instructions |
| Integer | N | 7, 9–255 | 1 | 16-bit signed integers |
| Floating point | F | 8, 9–255 | 2 | 32-bit IEEE-754 floating-point values |
| String | ST | 9–255 | 42 | ASCII strings |
| Long word | L | 9–255 | 2 | 32-bit signed integers |
| Message | MG | 9–255 | 25 | MSG instruction control blocks |
| PID | PD | 9–255 | 23 | PID instruction control blocks |
Source: MicroLogix 1400 Instruction Set Reference Manual, 1766-RM001J-EN-P (June 2023), Table 11. ASCII (A), programmable limit switch (PLS) and routing information (RI, RIX) files are also available and are omitted here for brevity.
Slot 0 is the controller’s embedded I/O, and slots 1 to 7 are expansion modules. A slash separates the bit, and a dot separates the word:
I:0/15: embedded input, word 0, bit 15O:0/4: embedded output, word 0, bit 4I:1/4: input module in expansion slot 1, bit 4O:2/7: output module in expansion slot 2, bit 7I:7.3: input module in slot 7, word 3 (for example, an analog channel)The data file number is optional in these short forms, so you will also see the full form, such as I1:0.0/0 for input file 1, slot 0, word 0, bit 0.
B3:0/5: bit file 3, word 0, bit 5. Many programs use B3 for internal relays.N7:12: integer file 7, element 12, a 16-bit signed value.F8:0: floating-point file 8, element 0, a 32-bit IEEE-754 value.T4:0.ACC, T4:0.PRE, T4:0/DN: accumulator, preset and done bit of timer 0.C5:1.ACC, C5:1/DN: accumulator and done bit of counter 1.ST9:0, L10:0: a string element and a long-word element in user-created files 9 and 10.Each timer is a 3-word element: a control word holding the EN, TT and DN bits, a preset and an accumulator. Preset and accumulator range from 0 to 32,767. The MicroLogix 1400 supports three time bases (0.001 s, 0.01 s and 1.00 s), so a 10-second delay is a preset of 10 at a 1.00 s time base or 1,000 at 0.01 s. Timer instructions are TON, TOF and the retentive RTO. Counters use CTU and CTD, and RES resets a timer or counter.
Bit-level instructions include XIC, XIO, OTE, OTL, OTU and the one-shots ONS, OSR and OSF. The XIC, OTE, OTL/OTU and ONS pages explain each one, and PLC timers and PLC counters cover the accumulator/preset model in depth.
Rockwell’s product description states that the MicroLogix 1400 is programmed with RSLogix 500 version 8.1 and above, as well as RSLogix Micro. Projects are saved as .RSS files. Studio 5000 Logix Designer, the tool for CompactLogix and ControlLogix, does not program MicroLogix controllers. Neither does Connected Components Workbench, the tool for Micro800.
RSLogix 500 and RSLogix Micro come in several editions, and Rockwell has offered free entry-level editions for some MicroLogix controllers. Which controllers each edition supports has changed over time, so check the current compatibility listing in Rockwell’s Product Compatibility and Download Center before assuming a free edition covers the 1400. Our RSLogix 500 free guide explains what to check, and RSLogix 500 vs Studio 5000 compares the two environments.
Rockwell’s migration guide also mentions RSLogix Emulate 500, its software emulator for RSLogix 500 projects, alongside the Micro800 Simulator used after migration. For hardware-free practice that does not depend on Rockwell licensing, see the RSLogix simulator page.
Online editing is supported on the MicroLogix 1400, which lets you change ladder logic while the controller runs. Treat it with the same care as any live change. Test in a safe state, follow your site’s management-of-change process, and keep an up-to-date offline copy of the program.
Not as of September 28, 2026. Rockwell’s MicroLogix family page still lists the MicroLogix 1400 as available. It says the MicroLogix 1100 and 1200 are discontinued and no longer available for sale, and it encourages customers on those models to migrate to Micro800. When we checked the 1766-L32BWA product page, its lifecycle status was Active Mature.
Rockwell defines its lifecycle statuses like this:
Active Mature is a signal to plan, not to panic. The controller is supported, but Rockwell has a newer platform in the same space. Lifecycle status is set per catalog number and can change, so look up each of your six possible part numbers, and your 1762 expansion modules, in the Product Lifecycle Status tool.
There are three realistic options. The right one depends on how long the machine will stay in service, whether it is growing, and which Rockwell platform the rest of your plant uses.
| Path | Software | Program conversion | Good fit when |
|---|---|---|---|
| Keep the MicroLogix 1400 | RSLogix 500 or RSLogix Micro (unchanged) | None | A stable machine with spares on hand and no need for more I/O, networking or new features. |
| Micro850 or Micro870 | Connected Components Workbench | MicroLogix to Micro800 Converter tool: ladder only, with a conversion report listing manual fixes | Small standalone machines where you want a current Rockwell micro controller with similar scale. |
| CompactLogix 5380 | Studio 5000 Logix Designer | Plan a rewrite into tags and routines; Rockwell’s Logix Designer Export targets SLC 500 and PLC-5 projects | Machines that are growing, need EtherNet/IP I/O and drives, integrated motion or safety, or must match a Studio 5000 plant standard. |
If the machine is stable, staying put is a legitimate choice. Make it a deliberate one. Save a current offline copy of the .RSS file with comments, record the catalog number and firmware, keep a tested spare controller, and consider a backup memory module so a replacement can be loaded quickly. Recheck the lifecycle status each year.
Rockwell’s migration guide (2080-RM002D, February 2026) maps each 1766 catalog number to a Micro850 (2080-L50E-24…) or Micro870 (2080-L70E-24…). It lists any plug-ins needed to match the 1400’s I/O. Use a Micro850 for up to four expansion modules and a Micro870 for more. If the relay outputs on a BXB or BXBA model are in use, add relay modules such as a 2080-OW4I plug-in or 2085-OW8 expansion module. The analog models need an analog plug-in. Integrated Architecture Builder 9.8.2.2 and later can migrate the MicroLogix 1400 hardware configuration to Micro850 and Micro870.
If the machine needs more I/O, EtherNet/IP drives and remote I/O, integrated motion, safety, or has to match a Studio 5000 plant standard, CompactLogix 5380 is the usual step. It is a bigger change: the program becomes tag-based. Rockwell’s Logix Designer Export feature is documented for PLC-5 and SLC 500 projects, and its manual notes that it does not support MicroLogix. Plan for a structured rewrite, or confirm current tooling with Rockwell. See CompactLogix vs ControlLogix.
Rockwell’s MicroLogix to Micro800 Converter tool (version 5.07, supported in Connected Components Workbench version 23 per the migration guide) is downloaded separately from the Product Compatibility and Download Center. It converts an RSLogix 500 or RSLogix Micro .RSS project into a Connected Components Workbench project. It handles ladder diagram only. Most instructions convert, some are replaced by Rockwell-supplied user-defined function blocks such as RA_TON_MICROLOGIX, and anything that needs manual work is logged in a conversion report.
Data files become arrays and I/O becomes named variables. The guide’s examples map N7:500 to N7[500], T4:6 to T4[6], I:0/5 to _IO_EM_DI_05 and O:0/4 to _IO_EM_DO_04. The logic survives, but every address in your documentation, HMI tags and messaging changes. Budget time to retest each sequence on the new controller before it goes back into production.
If you maintain MicroLogix equipment, most of the skill is reading and reasoning about ladder logic, which you can practice without a controller. The Allen-Bradley PLC simulator on this site has an Allen-Bradley-style learning dialect that accepts tags declared on MicroLogix-style I:0/0 and O:0/0 addresses. It supports XIC, XIO, OTE, OTL, OTU, TON, TOF, CTU and CTD:
TAG START_PB I:0/0 BOOL
TAG STOP_PB I:0/1 BOOL // stop button wired normally closed
TAG MOTOR O:0/0 BOOL
[XIC START_PB OR XIC MOTOR] XIC STOP_PB OTE MOTORRun it against the motor start/stop or conveyor sort scenario and the simulator checks the behavior, not just the syntax. Ladder logic examples and seal-in rungs explained are good companions.
Know the limits. The simulator is independent and is not RSLogix 500 or RSLogix Micro. It does not open .RSS files, emulate MicroLogix firmware, go online with a controller, or model data files such as B3, T4, C5 and N7. It does not support RTO, ONS, OSR or RES. Use it to build fluency, then confirm real programs in Rockwell’s software. The limitations page has the full list.
A free account includes 27 practice records and the first 6 core lessons in each dialect, including Allen-Bradley.
Specifications, lifecycle status and migration details come from Rockwell Automation’s own publications and pages, accessed on September 28, 2026. Recheck them for your catalog numbers before you buy or migrate.
Practice seal-ins, timers and counters with MicroLogix-style I/O addresses in your browser. No RSLogix license and no controller needed.
Allen-Bradley, Rockwell Automation, MicroLogix, Micro800, Micro850, Micro870, CompactLogix, RSLogix, RSLogix Emulate, Connected Components Workbench, Integrated Architecture Builder and Studio 5000 are trademarks of Rockwell Automation, Inc. PLC Simulator is independent and is not affiliated with, endorsed by or sponsored by Rockwell Automation.