Features
a174 Integrated SRAM, real-time
clock, CPU supervisor, crystal,
power-fail control circuit, and
battery
a174 Real-Time Clock counts hun-
dredths of seconds through years
in BCD format
a174 RAM-like clock access
a174 Compatible with industry-
standard 512K x 8 SRAMs
a174 Unlimited write cycles
a174 10-year minimum data retention
and clock operation in the ab-
sence of power
a174 Automatic power-fail chip dese-
lect and write-protection
a174 Watchdog timer, power-on reset,
alarm/periodic interrupt, power-
fail and battery-low warning
a174 Software clock calibration for
greater than ±1 minute per
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–
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 VCC 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 VCC.
1
bq4852Y
Aug. 1996
RTC Module With 512Kx8 NVSRAM
1
PN485201.eps
36-Pin DIP Module
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
RST
NC
A
18
A
16
A
14
A
12
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
DQ
1
DQ
2
V
SS
DQ
0
V
CC
NC
INT
A
15
A
17
WE
A
13
A
8
A
9
A
11
OE
A
10
CE
DQ
7
DQ
5
DQ
4
DQ
3
DQ
6
Pin Names
A0–A18 Address input
CE Chip enable
RST Microprocessor reset
WE Write enable
OE Output enable
DQ0–DQ7 Data in/data out
INT Programmable interrupt
VCC +5 volts
VSS Ground
Pin Connections