bq4842Y

The bq4842Y RTC Module is a nonvolatile 1,048,576-bit SRAM organized as 131,072 words by 8 bits with an integral accessible real-time clock and CPU supervisor. The CPU supervisor provides a programmable watchdog timer and a microprocessor reset. Other features include alarm,power-fail,and periodic interrupts,andabattery-lowwarning.


The bq4842Y combines an internal lithium battery, quartz crystal, clock and power-fail chip, and a full CMOS SRAM in a plastic 32-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 bq4842Y are located in registers 1FFF0h1FFFFhofthememoryarray.


The clock and alarm registers of bq4842Y are dual-port read/write SRAM locations that are updated once per second by a clock control circuit from the internal clock counters. The dual-port registers allow clock updates to occur without interrupting normal access to the rest of the SRAMarray.


The bq4842Y also contains a powerfail-detect circuit. The circuit deselects the device whenever V_CC falls below tolerance,providing a high degree of data security. The battery is electrically isolated when shipped from the factory to provide maximum battery capacity. The battery remains disconnected until the first applicationofV_CC.