bq4852Y
RTC Module With 512Kx8 NVSRAM
Features
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Integrated SRAM, real-time
clock, CPU supervisor, crystal,
power-fail control circuit, and
battery
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Real-Time Clock counts hun-
dredths of seconds through years
in BCD format
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RAM-like clock access
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Compatible with industry-
standard 512K x 8 SRAMs
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Unlimited write cycles
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10-year minimum data retention
and clock operation in the ab-
sence of power
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Automatic power-fail chip dese-
lect and write-protection
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Watchdog timer, power-on reset,
alarm/periodic interrupt, power-
fail and battery-low warning
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Software clock calibration for
g r e a t e r t ha n
鹵
1 m inut e pe r
month accuracy
General Description
The bq4852Y RTC Module is a non-
volatile 4,194,304-bit SRAM organ-
ized as 524,288 words by 8 bits with
an integral accessible real-time
clock and CPU supervisor. The CPU
supervisor provides a programmable
watchdog timer and a microproces-
sor reset. Other features include
alarm, power-fail, and periodic inter-
rupts, and a battery-low warning.
The device combines an internal lith-
ium battery, quartz crystal, clock and
power-fail chip, and a full CMOS
SRAM in a plastic 36-pin DIP mod-
ule. The RTC Module directly re-
places industry-standard SRAMs and
also fits into many EPROM and EE-
PROM sockets without any require-
ment for special write timing or limi-
tations on the number of write cycles.
Registers for the real-time clock,
alarm and other special functions
are located in registers 7FFF0h鈥?/div>
7FFFFh of the memory array.
The clock and alarm registers are
dual-port read/write SRAM loca-
tions that are updated once per sec-
ond by a clock control circuit from
the internal clock counters. The
dual-port registers allow clock up-
dates to occur without interrupting
normal access to the rest of the
SRAM array.
The bq4852Y also contains a power-
fail-detect circuit. The circuit dese-
lects the device whenever V
CC
falls
below tolerance, providing a high de-
gree of data security. The battery is
electrically isolated when shipped
from the factory to provide maxi-
mum battery capacity. The battery
remains disconnected until the first
application of V
CC
.
Pin Connections
RST
NC
A18
A16
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
VSS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
VCC
NC
INT
A15
A17
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
Pin Names
A
0
鈥揂
18
CE
RST
WE
OE
DQ
0
鈥揇Q
7
INT
V
CC
V
SS
Address input
Chip enable
Microprocessor reset
Write enable
Output enable
Data in/data out
Programmable interrupt
+5 volts
Ground
36-Pin DIP Module
PN485201.eps
Aug. 1996
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