PRELIMINARY
DS1557
4MEG NV Y2KC Timekeeping RAM
www.dalsemi.com
FEATURES
Integrated NV SRAM, real time clock, crystal,
power-fail control circuit and lithium energy
source
Clock registers are accessed identically to the
static RAM; these registers are resident in the
16 top RAM locations
Century byte register; i.e., Y2K complaint
Totally nonvolatile with over 10 years of
operation in the absence of power
Precision power-on reset
Programmable watchdog timer and RTC alarm
BCD coded year, month, date, day, hours,
minutes, and seconds with automatic leap year
compensation valid up to the year 2100
Battery voltage level indicator flag
Power-fail write protection allows for
±10%
V
CC
power supply tolerance
Lithium energy source is electrically
disconnected to retain freshness until power is
applied for the first time
PIN ASSIGNMENT
IRQ/FT
A15
A16
RST
V
CC
WE
OE
CE
DQ7
DQ6
DQ5
DQ4
DQ3
DQ2
DQ1
DQ0
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
A18
A17
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
X1
GND V
BAT
X2
34-Pin POWERCAP MODULE BOARD
(USES DS9034PCX POWERCAP)
PIN DESCRIPTION
A0-A14
DQ0-DQ7
IRQ
\FT
RST
CE
OE
WE
ORDERING INFORMATION
(5-Volt)
-70
70 ns access
-100 100 ns access
*DS1557WP-XXX (3.3 Volt)
-120 120 ns access
-150 150 ns access
*DS9034PCX (PowerCap) Required:
must be ordered seperately
DS1557P-XXX
V
CC
GND
NC
X1, X2
V
BAT
- Address Input
- Data Input/Outputs
- Interrupt, Frequency Test
Output (Open Drain)
- Power-On Reset Output
(Open Drain)
- Chip Enable
- Output Enable
- Write Enable
- Power Supply Input
- Ground
- No Connection
- Crystal Connection
- Battery Connection
DESCRIPTION
The DS1557 is a full function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) with a RTC
alarm, watchdog timer, power-on reset, battery monitor, and 512k x 8 non-volatile static RAM. User
access to all registers within the DS1557 is accomplished with a bytewide interface as shown in Figure 1.
The RTC Registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour
BCD format. Corrections for day of month and leap year are made automatically.
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012700
DALLAS [ DALLAS SEMICONDUCTOR ]
