参数：
VCC (Min) (V) 4.5
VCC (Max) (V) 5.5
Iq (Typ) (uA) 0.5
Features External SRAM control， Integrated CPU supervisor， Parallel bus interface， 16 RTC bytes
Rating Catalog
Operating temperature range (C) 0 to 70
封装|引脚|尺寸：
SOIC (DW) 28 184 mm2 17.9 x 10.3
特性：
Real-Time Clock counts seconds through years in BCD format
On-chip battery-backup switchover circuit with nonvolatile control for external SRAM
Less than 500nA of clock operation current in backup mode
Microprocessor reset valid to VCC =VSS
Independent watchdog timer with a programmable time-out period
Power-fail interrupt warning
Programmable clock alarm interrupt active in battery-backup mode
Programmable periodic interrupt
Battery-low warning
描述：
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， data loggers， and_computers.
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 (CE\OUT) 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 information 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 VCC 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 watchdog timer.
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 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 30.5us to 500ms.
