DS1244Y
DS1244Y
256K NV SRAM with Phantom Clock
FEATURES
PIN ASSIGNMENT
A14/RST
A12
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
V
CC
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
•
Real time clock keeps track of hundredths of seconds,
minutes, hours, days, date of the month, months, and
years
•
32K
x 8 NV SRAM directly replaces volatile static
RAM or EEPROM
eration and retains RAM data
•
Embedded lithium energy cell maintains calendar op-
•
Watch function is transparent to RAM operation
•
Month and year determine the number of days in each
month; volid up to 1200
•
Standard 28–pin JEDEC pinout
•
Full 10% operating range
•
Operating temperature range 0°C to 70°C
•
Accuracy is better than
±1
minute/month @ 25°C
•
Over
10 years of data retention in the absence of
power
A
o
–A
14
CE
GND
DQ
0-
DQ
7
V
CC
WE
OE
NC
RST
28–PIN ENCAPSULATED PACKAGE
740 MIL EXTENDED
PIN DESCRIPTION
–
–
–
–
–
–
–
–
–
Address Inputs
Chip Enable
Ground
Data In/Data Out
Power (+5V)
Write Enable
Output Enable
No Connect
Reset
•
Available in 120, 150 and 200 ns access time
ORDERING INFORMATION
DS1244Y–XXX
–120
–150
DS1244Y
120 ns access
150 ns access
200 ns access
DESCRIPTION
The DS1244Y 256K NV SRAM with Phantom Clock is a
fully static nonvolatile RAM (organized as 32,768 words
by 8 bits) with a built–in real time clock. The DS1244Y
has a self–contained lithium energy source and control
circuitry which constantly monitors V
CC
for an out–of–
tolerance condition. When such a condition occurs, the
lithium energy source is automatically switched on and
write protection is unconditionally enabled to prevent
garbled data in both the memory and real time clock.
The Phantom Clock provides timekeeping information
including hundredths of seconds, seconds, minutes,
hours, day, date, month, and year information. The date
at the end of the month is automatically adjusted for
months with less than 31 days, including correction for
leap years. The Phantom Clock operates in either
24–hour or 12–hour format with an AM/PM indicator.
ECopyright
1997 by Dallas Semiconductor Corporation.
All Rights Reserved. For important information regarding
patents and other intellectual property rights, please refer to
Dallas Semiconductor data books.
032697 1/12
DALLAS [ DALLAS SEMICONDUCTOR ]
