Dallas Semiconductor DS1691, DS1688S, DS1688 Datasheet
DS1688/DS1691
DS1688/DS1691
3 Volt/5 Volt Serialized Real Time Clock
with NV RAM Control
FEATURES
Incorporates industry standard DS1287 PC clock plus
enhanced features:
• +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
12.5 pF crystal
• 114 bytes user NVRAM
• Auxiliary battery input
• RAM clear input
• Century register
• 32 KHz output for power management
• 32–bit V
• 32–bit V
powered elapsed time counter
CC
powered elapsed time counter
BAT
• 16–bit power cycle counter
• Compatible with existing BIOS for original DS1287
functions
• Available as chip (DS1688) or stand–alone module
with embedded battery and crystal (DS1691)
• Timekeeping algorithm includes leap year compensa-
tion valid up to 2100
ORDERING INFORMATION
PART # DESCRIPTION
DS1688 RTC Chip, 28–pin DIP
DS1688S RTC Chip, 28–pin SOIC
DS1691 RTC Module; 28–pin DIP
PIN ASSIGNMENT
V
BAUX
X1
X2
RCLR
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
PWR
GND
DS1688 28–PIN DIP
28
1
27
2
26
3
25
4
24
5
23
6
22
7
21
8
20
9
19
10
18
11
17
12
16
13
15
14
(600 MIL)
V
BAUX
NC
NC
RCLR
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
PWR
GND
DS1691 28–PIN ENCAPSU-
LATED PACKAGE (740 MIL)
CEI
CEO
V
CCI
V
CCO
SQW
V
BAT
IRQ
PSEL
RD
GND
WR
ALE
CS
KS
V
1
2
3
4
5
6
7
8
9
10
11
12
13
14
BAUX
X1
X2
RCLR
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
PWR
GND
DS1688S 28–PIN SOIC
CEI
28
CEO
27
V
26
CCI
V
25
CCO
SQW
24
NC
23
IRQ
22
PSEL
21
RD
20
NC
19
WR
18
ALE
17
CS
16
KS
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
(330 MIL)
PIN DESCRIPTION
X1 – Crystal Input
X2 – Crystal Output
RCLR – RAM Clear Input
AD0-AD7 – Mux’ed Address/Data Bus
PWR
KS – Kickstart Input
CS – RTC Chip Select Input
ALE – RTC Address Strobe
WR
RD
V
CCO
– Power–on Interrupt Output
– RTC Write Data Strobe
– RTC Read Data Strobe
– RAM Power Supply Output
28
CEI
27
CEO
26
V
CCI
25
V
CCO
24
SQW
23
V
BAT
22
IRQ
21
PSEL
20
RD
19
GND
18
WR
17
ALE
16
CS
15
KS
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DS1688/DS1691
IRQ – Interrupt Request Output
SQW – Square Wave Output
V
CCI
– +3 or +5 Volt Main Supply
GND – Ground
V
V
BAT
BAUX
– Battery + Supply
– Auxiliary Battery Supply
PSEL – +3 or +5 Volt Power Select
CEI
– RAM Chip Enable In
CEO – 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, 1 14 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
gered 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.
output pin can be trig-
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 V
and CEO pins. The
CCO
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 V
put to RAM (CEO
) is controlled during power transients to
pin. The chip enable out-
CCO
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 V
is guaranteed.
CC
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, t
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.
, after a power–up
REC
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