The 1764-MM2RTC is a memory and real-time clock module, designed and manufactured by Allen-Bradley. It belongs to the MicroLogix 1550 series. This unit is fully compatible with all the MicroLogix processors and controllers. This module includes a memory module of 16K and a real-time clock. This memory module is essential when it comes to using programs such as the RSLogix 500 on its 5.10.00 version, or higher, that requires a large memory. Also, the memory module support backups programs and other functions 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 an executing mode, the module will not be recognized until a power cycle occurs or the controller enters in a non-executing 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 is a memory and real-time clock module 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 1764-MM2RTC is a memory and real-time clock module has an internal and permanent battery. It also features a battery indicator. When the battery fails the module needs to be replaced. One way to preserve the battery of the module is to use the disable clock button while the controller is in the storage stage. Battery life expectancy is approximately of 5 years while it operates at a temperature range of 0 to 40 degrees Celsius (32 to 104 degrees Fahrenheit).