The Dallas Phantom Real Time Clocks are a family of devices that offer the combination of a transparent CMOS timekeeper and a nonvolatile static RAM meeting the standard JEDEC bytewide pinouts. Some varieties of the Dallas Phantom Real Time Clocks also provide a transparent CMOS timekeeper for use with ROM. The timekeeper is transparent to the RAM/ROM memory map because it does not occupy any of the existing RAM/ROM locations. These devices are termed “Phantom” because the timekeeper is accessed only when a predetermined 64–bit pattern has been received by the device. When the timekeeper is not being accessed, the RAM/ROM can be accessed normally. The timekeeper keeps track of hundredths of seconds, seconds, minutes, hours, day, date, month, and year information. In the absence of power, a lithium energy source maintains the timekeeping operation and retains data in the CMOS static RAM.