DALLAS DS1691

DS1688/DS1691
DS1688/DS1691
3 Volt/5 Volt Serialized Real Time Clock
with NV RAM Control
FEATURES
PIN ASSIGNMENT
Incorporates industry standard DS1287 PC clock plus
enhanced features:
VBAUX
1
28
CEI
VBAUX
1
28
CEI
X1
2
27
CEO
X1
2
27
CEO
X2
3
26
VCCI
X2
3
26
VCCI
RCLR
4
25
VCCO
RCLR
4
25
VCCO
AD0
5
24
SQW
AD0
5
24
SQW
AD1
6
23
VBAT
AD1
6
23
VBAT
AD2
7
22
IRQ
AD2
7
22
IRQ
AD3
8
21
PSEL
AD3
8
21
PSEL
AD4
9
20
RD
AD4
9
20
RD
AD5
10
19
GND
AD5
10
19
GND
AD6
11
18
WR
AD6
11
18
WR
AD7
12
17
ALE
AD7
12
17
ALE
PWR
13
16
CS
PWR
13
16
CS
GND
14
15
KS
GND
14
15
KS
• +3
or +5 volt operation
• 64–bit Silicon serial number
• 64–bit
customer specific ROM or additional serial
number available
• Power
control circuitry supports system power on
from date/time alarm or key closure
• Automatic
battery backup and write protection to
external SRAM
• Crystal select bit allows RTC to operate with 6 pF or
DS1688 28–PIN DIP
(600 MIL)
DS1688S 28–PIN SOIC
(330 MIL)
12.5 pF crystal
VBAUX
1
28
CEI
NC
2
27
CEO
NC
3
26
VCCI
RCLR
4
25
• RAM clear input
VCCO
AD0
5
24
SQW
• Century register
AD1
6
23
NC
AD2
7
22
IRQ
• 32 KHz output for power management
AD3
8
21
PSEL
AD4
9
20
RD
• 32–bit VCC powered elapsed time counter
AD5
10
19
NC
• 32–bit VBAT powered elapsed time counter
AD6
11
18
WR
AD7
12
17
ALE
PWR
13
16
CS
GND
14
15
KS
• 114 bytes user NVRAM
• Auxiliary battery input
• 16–bit power cycle counter
• Compatible with
existing BIOS for original DS1287
DS1691 28–PIN ENCAPSULATED PACKAGE (740 MIL)
functions
• Available as chip (DS1688) or stand–alone module
with embedded battery and crystal (DS1691)
• Timekeeping algorithm includes leap year compensation valid up to 2100
ORDERING INFORMATION
PART #
DS1688
DS1688S
DS1691
DESCRIPTION
RTC Chip, 28–pin DIP
RTC Chip, 28–pin SOIC
RTC Module; 28–pin DIP
PIN DESCRIPTION
X1
X2
RCLR
AD0-AD7
PWR
KS
CS
ALE
WR
RD
VCCO
–
–
–
–
–
–
–
–
–
–
–
Crystal Input
Crystal Output
RAM Clear Input
Mux’ed Address/Data Bus
Power–on Interrupt Output
Kickstart Input
RTC Chip Select Input
RTC Address Strobe
RTC Write Data Strobe
RTC Read Data Strobe
RAM Power Supply Output
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DS1688/DS1691
IRQ
SQW
VCCI
GND
VBAT
VBAUX
PSEL
CEI
CEO
–
–
–
–
–
–
–
–
–
Interrupt Request Output
Square Wave Output
+3 or +5 Volt Main Supply
Ground
Battery + Supply
Auxiliary Battery Supply
+3 or +5 Volt Power Select
RAM Chip Enable In
RAM Chip Enable Out
DESCRIPTION
The DS1688/DS1691 is a real time clock (RTC) designed as a successor to the industry standard DS1285,
DS1385, DS1485, and DS1585 PC real time clocks.
This device provides the industry standard DS1285
clock function with the new feature of either +3.0 or +5.0
volt operation and automatic backup and write protection to an external SRAM. The DS1688 also incorporates a number of enhanced features including a silicon
serial number, power on/off control circuitry, 114 bytes of
user NVSRAM, power on elapsed timer, and power
cycle counter.
Each DS1688/DS1691 is individually manufactured
with a unique 64–bit serial number as well as an additional 64–bit customer specific ROM or serial number.
The serial number is programmed and tested at Dallas
to insure that no two devices are alike. The serial number can be used to electronically identify a system for
purposes such as establishment of a network node address or for maintenance tracking. Blocks of available
numbers from Dallas Semiconductor can be reserved
by the customer.
The serialized RTC’s also incorporate power control circuitry which allows the system to be powered on via an
external stimulus, such as a keyboard or by a time and
date (wake up) alarm. The PWR output pin can be triggered by one or either of these events, and can be used
to turn on an external power supply. The PWR pin is under software control, so that when a task is complete,
the system power can then be shut down.
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The DS1688/DS1691 incorporates a power on elapsed
time counter, a power on cycle counter, and a battery
powered continuous counter. These three counters
provide valuable information for maintenance and warranty requirements.
Automatic backup and write protection for an external
SRAM is provided through the VCCO and CEO pins. The
lithium energy source used to permanently power the real
time clock is also used to retain RAM data in the absence
of VCC power through the VCCO pin. The chip enable output to RAM (CEO) is controlled during power transients to
prevent data corruption.
The DS1688 is a clock/calendar chip with the features
described above. An external crystal and battery are
the only components required to maintain time–of–day
and memory status in the absence of power. The
DS1691 incorporates the DS1688 chip, a 32.768 KHz
crystal, and a lithium battery in a complete, self–contained timekeeping module. The entire unit is fully
tested at Dallas Semiconductor such that a minimum of
10 years of timekeeping and data retention in the
absence of VCC is guaranteed.
For a complete description of operating conditions,
electrical characteristics, bus timing, and pin descriptions other than the SQW output, see the
DS1689/DS1693 data sheet.
SIGNAL DESCRIPTION
SQW (Square Wave Output) – The SQW output signal
functions identical to the DS1689/DS1693 with an
exception occurring at power–up. A 32 KHz square
wave will be output on this pin, tREC, after a power–up
condition has been detected. This condition sets the following bits enabling the 32 KHz output; DV1=1,
SQWE=1, and E32K=1. The square wave will be output
on this pin if either SQWE=1 or E32K=1.
DS1688/DS1691
DS1688 28–PIN DIP
PKG
MIN
MAX
A IN.
MM
1.445
36.70
1.470
37.34
B IN.
MM
0.530
13.46
0.550
13.97
C IN.
MM
0.140
3.56
0.160
4.06
D IN.
MM
0.600
15.24
0.625
15.88
E IN.
MM
0.015
0.38
0.040
1.02
F IN.
MM
0.120
3.05
0.145
3.68
C
G IN.
MM
0.090
2.29
0.110
2.79
F
H IN.
MM
0.625
15.88
0.675
17.15
J IN.
MM
0.008
0.20
0.012
0.30
K IN.
MM
0.015
0.38
0.022
0.56
B
D
1
A
K
G
E
28–PIN
DIM
J
H
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DS1688/DS1691
DS1688S 28–PIN SOIC
K
G
PKG
28–PIN
DIM
MIN
MAX
A IN.
MM
0.706
17.93
0.728
18.49
B IN.
MM
0.338
8.58
0.350
8.89
C IN.
MM
0.086
2.18
0.110
2.79
D IN.
MM
0.020
0.58
0.050
1.27
E IN.
MM
0.002
0.05
0.014
0.36
F IN.
MM
0.090
2.29
0.124
3.15
G IN.
MM
0.050
1.27
H IN.
MM
0.460
11.68
0.480
12.19
J IN.
MM
0.006
0.15
0.013
0.33
K IN.
MM
0.014
0.36
0.020
0.51
BSC
C
A
E
B
F
0–8 deg. typ.
J
H
D
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DS1688/DS1691
DS1691 28–PIN 740 MIL MODULE
15
28
PKG
1
14
A
C
E
F
D
K
G
13 EQUAL SPACES AT
.100 ± .010 TNA
NOTE:
28–PIN
DIM
MIN
MAX
A IN.
MM
1.520
38.61
1.540
39.12
B IN.
MM
0.695
17.65
0.740
18.80
C IN.
MM
0.350
8.89
0.375
9.52
D IN.
MM
0.100
2.54
0.130
3.30
E IN.
MM
0.015
0.38
0.030
0.76
F
IN.
MM
0.110
2.79
0.140
3.56
G IN.
MM
0.090
2.29
0.110
2.79
H IN.
MM
0.590
14.99
0.630
16.00
J
IN.
MM
0.008
0.20
0.012
0.30
K IN.
MM
0.015
0.38
0.021
0.53
PINS 2, 3, 19 AND 23 ARE MISSING BY DESIGN.
J
H
B
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