The Allen-Bradley 1764-LSP, also cataloged as the 1764-LSP/C Processor Module, executes ladder scan, I/O ownership and local 1769 expansion-bus arbitration within a MicroLogix 1500 base unit.

Catalog Number And Variant Notes

The base catalog number 1764-LSP denotes the standard MicroLogix 1500 processor. The suffix "/C" in 1764-LSP/C marks a later hardware/series track; it does not convert the module into the high-performance 1764-LRP. The 1764-LRP adds a second configurable RS-232 channel, data log/recipe memory and larger user program space. A 1764-LSP cannot be field-upgraded into an LRP by firmware alone; the channel hardware and memory map differ.

Electrical & Mechanical Data

MicroLogix Local Expansion Bus And Firmware Limits

The 1764-LSP drives the proprietary MicroLogix 1500 local expansion connector on the rear of the processor, not a ControlLogix backplane and not an EtherNet/IP deterministic switch fabric. Up to eight 1769 Compact I/O modules can be addressed on a properly powered local expansion chain before the 5 VDC bus current budget is exceeded; further I/O density requires offloading to DeviceNet nodes through a 1769-SDN scanner rather than stacking more local modules. RSLogix 500 is the native programming environment; OS/firmware major revisions on 1764-LSP/C are bound to the project file revision saved by the offline editor, so a newer processor will reject an older protected project until the source ACS/RSS is reopened and re-saved at the matched revision.

Ordering Information

• 1 x 1764-LSP processor module, series as shipped (commonly 1764-LSP/C)
• 1 x removable product label / catalog tag
• 1 x installation and replacement note, MicroLogix 1500 processor swap section
• 1 x 1764-BAT or equivalent backup battery if ordered separately for user-memory retention during power loss

Base Unit And Replacement Practice

• Install the 1764-LSP only into a 1764-24AWA, 1764-24BWA or 1764-28BXB MicroLogix 1500 base; the processor keys and expansion edge connector are not mechanically compatible with 1762 or 1769 sole-controller slots.
• Remove AC or DC supply from the base before extracting the processor. The MicroLogix 1500 local expansion bus is not specified for live processor hot-swap; pulling the CPU under scan can drop the I/O image and force a cold restart on re-seat.
• Route the single processor communication cable away from 24 VDC output flyback lines and relay coil commons; the ML1500 base has no optical isolation between low-level logic reference and the integrated I/O commons on AC-relay bases.
• Verify battery presence before long storage. With no backup battery, volatile user program/data RAM is lost on removal from the base, even though the non-volatile load image may still reside in the stored project file on the engineering PC.

Technical Q&A

• Is 1764-LSP interchangeable with 1764-LRP in the same base?

No. Both plug into the same MicroLogix 1500 base mechanically, but the LRP carries a second configurable serial channel and a larger memory map. Moving an LRP project into an LSP base aborts compile or download on insufficient user words; moving an LSP project into an LRP works only if no LRP-only instruction or extra channel is referenced.

• Can the 1764-LSP communicate on EtherNet/IP directly?

Not natively. The 1764-LSP has no embedded Ethernet MAC. Ethernet access is achieved through an external gateway such as 1761-NET-ENI on the serial side, or by placing 1769-ECR/1769-ENBT on a separate CompactLogix-class chassis, not by bridging through the ML1500 local expansion bus itself.

• What happens if 300 mA at 5 VDC is exceeded on the local bus?

The 300 mA figure is the processor self-draw from the base 5 VDC rail; it is not the full expansion budget. If total local 1769 module draw plus processor draw exceeds the 1764 base power supply capacity, the leftmost under-powered module drops its I/O and the processor logs a non-fatal fault until the overload is removed.

• Does the processor retain the program without a battery?

Partially. User logic and data reside in battery-backed RAM on the 1764-LSP. With a failed or absent 1764-BAT, a power cycle clears RAM. Recover the running image only from the last RSLogix 500 offline/project file or from a previously saved memory module transfer, not from the processor silicon.

• Is online program edit supported on 1764-LSP?

Yes, within RSLogix 500 online edit limits for MicroLogix 1500 standard processors. Edits are scanned into the active ladder image after acceptance, but large rung insertions near the 7.65K user-word ceiling may be rejected until memory is re-partitioned or unused data-table files are shortened.

• Can a 1764-LSP be replaced while the machine is running?

Not recommended. Unlike some ControlLogix redundant pairs, the MicroLogix 1500 single-processor architecture has no standby CPU. Removing the 1764-LSP stops the scan cycle; all integrated and local expansion I/O enter their safe/off-state until the replacement processor is seated, powered and placed in Run/Remote Run.

• What cable is used for the DF1 / DH-485 port on 1764-LSP?

For point-to-point DF1 full-duplex, a 1761-CBL-PM02 or shielded null-modem RS-232 cable is used between PC COM/USB adapter and the processor port. For DH-485 multidrop, the 1761-NET-AIC isolator converts the RS-232 port to RS-485 and enforces the 120 ohm termination at the physical ends of the trunk.

• Is there a direct Rockwell successor for 1764-LSP?

Rockwell lists 1764-LSP as discontinued since Jun 2017. Migration paths are normally evaluated toward 1769-L3x CompactLogix or 5069 CompactLogix, but this is not pin- or base-compatible; it requires rewiring the I/O terminations, re-mapping 1769 local modules and converting the RSLogix 500 project to Studio 5000, not a drop-in processor swap.