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BQ4845P-N

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德州仪器 - TI 外围集成电路光电二极管监控双倍数据速率时钟
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描述
Parallel RTC With CPU Supervisor

BQ4845P-N 数据手册

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bq4845/bq4845Y  
Parallel RTC With CPU Supervisor  
tects an out-of-tolerance condition, it  
generates an interrupt warning and  
General Description  
Features  
Real-Time Clock counts seconds  
The bq4845 Real-Time Clock is a  
low-power microprocessor periph-  
eral 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 ma-  
chines, copiers, industrial control  
syst em s, poin t -of-sa le t er m in a ls,  
data loggers, and computers.  
subsequently a microprocessor reset.  
The reset stays active for 200ms after  
VCC rises within tolerance, to allow for  
power supply and processor stabiliza-  
tion.  
through years in BCD format  
On-chip battery-backup switchover  
circuit with nonvolatile control for  
external SRAM  
Th e bq4845 a ls o h a s a bu ilt -in  
watchdog timer to monitor processor  
operation. If the microprocessor does  
not toggle the watchdog input (WDI)  
within the programmed time-out pe-  
riod, the bq4845 asserts WDO and  
RST. WDI unconnected disables the  
watchdog timer.  
Less than 500nA of clock opera-  
tion current in backup mode  
Microprocessor reset valid to  
The bq4845 provides direct connec-  
tions for a 32.768KHz quartz crystal  
and a 3V backup battery. Through  
the use of the conditional chip en-  
a ble ou t pu t (CE OUT) a n d ba t t er y  
volt a ge ou t pu t (VOU T) p in s, t h e  
bq4845 can write-protect and make  
n on vola t ile external SRAMs. The  
ba cku p cell powers t he rea l-t im e  
clock and maintains SRAM infor-  
m a t ion in t h e a bsen ce of syst em  
voltage.  
VCC = VSS  
I n d ep en d en t wa t ch d og t im er  
with a programmable time-out  
period  
The bq4845 can generate other in-  
terrupts based on a clock alarm con-  
dit ion or a per iodic set t in g. Th e  
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 inter-  
rupts at a rate beyond once per sec-  
ond, the periodic interrupt can be pro-  
grammed with periods of 30.5µs to  
500ms.  
Power-fail interrupt warning  
Programmable clock alarm inter-  
r u pt a ct ive in ba t t er y-ba cku p  
mode  
Programmable periodic interrupt  
Battery-low warning  
The bq4845 contains a temperature-  
compensated reference and comparator  
circuit that monitors the status of its  
voltage supply. When the bq4845 de-  
Pin Names  
Pin Connections  
A0–A3  
Clock/control address  
inputs  
BC  
Backup battery input  
Back-up battery output  
Interrupt output  
Microprocessor reset  
Watchdog input  
Watchdog output  
+5V supply  
V
28  
1
V
CC  
OUT  
VOUT  
INT  
X
1
X
2
27  
26  
2
3
WE  
CE  
DQ0–DQ7 Data inputs/outputs  
IN  
4
CE  
BC  
WDO  
INT  
RST  
25  
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
OUT  
WE  
OE  
Write enable  
5
6
WDI  
OE  
RST  
WDI  
WDO  
VCC  
VSS  
Output enable  
Chip select input  
A
3
7
A
A
A
8
9
CS  
2
1
0
CS  
V
SS  
10  
11  
12  
13  
14  
DQ  
7
CEIN  
External RAM chip  
enable  
DQ  
DQ  
8
DQ  
5
0
DQ  
1
DQ  
2
DQ  
4
V
SS  
DQ  
3
CEOUT  
X1–X2  
Conditional RAM chip  
enable  
Ground  
28-DIP or SOIC  
PN484501.eps  
Crystal inputs  
Aug. 1995  
1

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