PRELIMINARY
DS1557
4MEG NV Y2KC Timekeeping RAM
www.dalsemi.com
FEATURES
PIN ASSIGNMENT
ꢀ
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
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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
IRQ/FT
A15
A16
RST
VCC
ꢀ
WE
OE
CE
ꢀ
ꢀ
A8
DQ7
DQ6
DQ5
DQ4
DQ3
A7
A6
A5
A4
A3
A2
A1
A0
ꢀ
ꢀ
ꢀ
Precision power-on reset
DQ2
DQ1
DQ0
GND
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%
VBAT X2
X1 GND
34-Pin POWERCAP MODULE BOARD
(USES DS9034PCX POWERCAP)
ꢀ
ꢀ
PIN DESCRIPTION
VCC power supply tolerance
A0-A14
DQ0-DQ7
IRQ \FT
- Address Input
- Data Input/Outputs
ꢀ
Lithium energy source is electrically
disconnected to retain freshness until power is
applied for the first time
- Interrupt, Frequency Test
Output (Open Drain)
RST
- Power-On Reset Output
(Open Drain)
ORDERING INFORMATION
DS1557P-XXX
(5-Volt)
-70
70 ns access
CE
OE
- Chip Enable
- Output Enable
-100 100 ns access
*DS1557WP-XXX (3.3 Volt)
-120 120 ns access
-150 150 ns access
*DS9034PCX (PowerCap) Required:
must be ordered seperately
WE
- Write Enable
- Power Supply Input
- Ground
- No Connection
- Crystal Connection
- Battery Connection
VCC
GND
NC
X1, X2
VBAT
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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