资 源 简 介
The Dallas Phantom Real Time Clocks are a family ofdevices that offer the combination of a transparentCMOS timekeeper and a nonvolatile static RAM meetingthe standard JEDEC bytewide pinouts. Some varietiesof the Dallas Phantom Real Time Clocks also providea transparent CMOS timekeeper for use with ROM.The timekeeper is transparent to the RAM/ROMmemory map because it does not occupy any of theexisting RAM/ROM locations. These devices aretermed “Phantom” because the timekeeper is accessedonly when a predetermined 64–bit pattern has beenreceived by the device. When the timekeeper is notbeing accessed, the RAM/ROM can be accessed normally.The timekeeper keeps track of hundredths ofseconds, seconds, minutes, hours, day, date, month,and year information. In the absence of power, a lithiumenergy source maintains the timekeeping operation andretains data in the CMOS static RAM.
