bq4822Y

The bq4822Y RTC Module is a nonvolatile 65,536-bit SRAM organized as 8192 words by 8 bits with an integral real-time clock and CPU supervisor. The CPU supervisor provides a programmable watchdog timer and a microprocessor reset.Other features include an alarm, power-fail and periodic interrupt, andabatterylowwarning.


The bq4822Y combines an internal lithium battery, quartz crystal, clock and power-fail chip, and a full CMOS SRAM in a plastic 28-pin DIP module. The RTC Module directly replaces industry-standard SRAMs and also fits into many EPROM and EEPROM sockets without any requirement for special write timing or limitations on the numberofwritecycles.


Registers for the real-time clock,alarm and other special functions of bq4822Y are located in registers 1FF0h1FFFhofthememoryarray.


The clock and alarm registers are dual-port read/write SRAM locations of bq4822Y that are updated once per second by a clock control circuit from the internal clock counters. The dual-port registers of bq4822Y allow clock updates to occur without errupting normal access to the rest of the SRAMarray.


The bq4822Y also contains a powerfail-detect circuit. The circuit deselects the device whenever V_CC falls below olerance,providing a high degree of data security. The battery of bq4822Y is electrically isolated when shipped from the factory to provide maxi-mum battery capacity. The battery remains disconnected until the first applicationofV_CC.