BQ4850Y_14 Datasheet, PDF (1/17 Pages) Texas Instruments – RTC Module With 512Kx8 NVSRAM

Not Recommended For New Designs
bq4850Y
RTC Module With 512Kx8 NVSRAM
Features
® Integrated SRAM, real-time
clock, crystal, power-fail control
circuit, and battery
® Real-Time Clock counts seconds
through years in BCD format
® RAM-like clock access
® Pin-compatible with industry-
standard 512K x 8 SRAMs
® Unlimited write cycles
® 10-year minimum data retention
and clock operation in the absence
of power
® Automatic power-fail chip dese-
lect and write-protection
® Software clock calibration for
greater than ±1 minute per
month accuracy
General Description
The bq4850Y 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.
The device combines an internal lith-
ium battery, quartz crystal, clock and
power-fail chip, and a full CMOS
SRAM in a plastic 32-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 7FFF8h–
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 bq4850Y 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.
Pin Connections
A18 1
A16 2
A14 3
A12 4
A7 5
A6 6
A5 7
A4 8
A3 9
A2 10
A1 11
A0 12
DQ0 13
DQ1 14
DQ2 15
VSS 16
32 VCC
31 A15
30 A17
29 WE
28 A13
27 A8
26 A9
25 A11
24 OE
23 A10
22 CE
21 DQ7
20 DQ6
19 DQ5
18 DQ4
17 DQ3
32-Pin DIP Module
PN485001.eps
SLUS057A- January 2005
Pin Names
A0–A18 Address input
CE
Chip enable
WE
Write enable
OE
Output enable
DQ0–DQ7 Data in/data out
VCC
+5 volts
VSS
Ground
1