Product Summary

The DS1644 is a 32k x 8 nonvolatile static RAM with a full function real time clock, which are bothaccessible in a byte-wide format. The nonvolatile timekeeping RAM is functionally equivalent to anyJEDEC standard 32k x 8 SRAM. The device can also be easily substituted for ROM, EPROM andEEPROM, providing read/write nonvolatility and the addition of the real time clock function. The realtime clock information resides in the eight uppermost RAM locations. The RTC registers contain year,month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for the day of themonth and leap year are made automatically. The RTC clock registers are double-buffered to avoid accessof incorrect data that can occur during clock update cycles. The double-buffered system also preventstime loss as the timekeeping countdown continues unabated by access to time register data. The DS1644also contains its own power-fail circuitry, which deselects the device when the VCC supply is in an out-of-tolerance condition. This feature prevents loss of data from unpredictable system operation brought on bylow VCC as errant access and update cycles are avoided.