The 1764-MM2RTC is a memory and real-time clock module, designed and manufactured by Allen-Bradley. It belongs to the MicroLogix 1500 series. This unit is fully compatible with MicroLogix 1764-LRP and 1764-LSP controllers. It includes a memory module of 16K and a real-time clock. This memory module is essential when for storing program that requires a large memory. Also, the memory module support backups programs and other functions such as data file download protection, program compare, among others. The 1764-MM2RTC memory/real-time clock module can be inserted or removed at any time without having the risk of damage to the module or the controller. If the module is installed while the controller is in RUN mode, the module will not be recognized until a power cycle occurs or the controller enters in a PROGAM or STOP mode. The function of the Real-time clock is to provide date and time information to the Real-time clock (RTC) function file in the controller. If the module is removed, the controller will write zeros to the RTC Function file.

The accuracy of the 1764-MM2RTC varies depending on the temperature. For example, for a temperature of 25 degrees Celsius (77 degrees Fahrenheit) the accuracy will be an approximate of +36 to -68 seconds per month.

The Allen-Bradley 1764-MM2RTC is a MicroLogix 1500 option module. This module is installed to a 1764-LRP or 1764-LSP controller to provide a non-volatile memory and real-time clock capability. The integrated memory of this module amount to 16KB which may be used to store programs, data, recipe, and data logs.

The Real-Time clock capability is an important feature especially in HVAC and BMS systems. Process equipment such as motors and compressors are ideally installed in duplex or triples sets where 1 unit is assigned as active and the other equipment as stand-by. For a triplex configuration, the Third equipment is usually the spare. By linking the user program to a Real-Time clock, equipment mode assignments may be automatically shifted with reference to the calendar and time provided by this module. This ensures that runtime is equally distributed to each equipment. This contributes to proper operation, better maintenance and a more reliable operation.

Real-time clock accuracy is dependent on the stability of the quartz crystal used over the operating temperature. For Temperature range 0°C (+32°F), the accuracy is +34 to -70 seconds/month. For +25°C (+77°F), +36 to -68 seconds/month. For +40°C (+104°F), +29 to -75 seconds/month and +55°C (+131°F), -133 to -237 seconds/month.

The integrated 16KB memory on the other hand provides a non-volatile memory that prevents unplanned program and data deletion. This event is typically triggered by voltage and current surges and battery drain. The memory used by the 1764-MM2RTC does not depend on the Lithium battery to retain its memory.