bq4845

The bq4845 Real-Time Clock is a low-power microprocessor peripheral that integrates a time-of-day clock, a 100-year calendar, and a CPU supervisor in a 28-pin SOIC or DIP. The bq4845 is ideal for fax machines, copiers, industrial control systems, point-of-sale terminals,dataloggers,andcomputers.


The bq4845 provides direct connections for a 32.768KHz quartz crystal and a 3V backup battery. Through the use of the conditional chip enable output (CEOUT) and battery voltage output (VOUT) pins, the bq4845 can write-protect and make nonvolatile external SRAMs. The backup cell powers the real-time clock and maintains SRAM infor-mation in the absence of system voltage.


The bq4845 contains a temperature-compensated reference and comparator circuit that monitors the status of its voltage supply. When the bq4845 detects an out-of-tolerance condition, it generates an interrupt warning and subsequently a microprocessor reset.The reset stays active for 200ms after V_CC rises within tolerance, to allow for power supply and processor stabilization.


The bq4845 also has a built-in watchdog timer to monitor processor operation.If the microprocessor does not toggle the watchdog input (WDI) within the programmed time-out period, the bq4845 asserts WDO and RST. WDI unconnected disables the watchdogtimer.


The bq4845 can generate other interrupts based on a clock alarm condition or a periodic setting. The alarm interrupt can be set to occur from once per second to once per month. The alarm of bq4845 can be made active in the battery-backup mode to serve as a system wake-up call. For interrupts at a rate beyond once per second,the periodic interrupt can be programmed with periods of 30.5sto 500ms.