DS1742
Y2KC Nonvolatile Timekeeping
RAM
www.maxim-ic.com
FEATURES
PIN CONFIGURATION
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 Eight Top RAM Locations
Century Byte Register
Totally Nonvolatile with Over 10 Years of
Operation in the Absence of Power
BCD Coded Century, 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%
VCC Power Supply Tolerance
Lithium Energy Source is Electrically
Disconnected to Retain Freshness until Power
is Applied for the First Time
Standard JEDEC Bytewide 2k x 8 Static RAM
Pinout
Quartz Accuracy ±1 Minute a Month at +25°C,
Factory Calibrated
UL Recognized
TOP VIEW
A7
A6
A5
A4
A3
A2
A1
A0
DQ0
DQ1
DQ2
GND
1
24
2
23
DS1742
3
22
4
21
5
20
6
19
7
18
8
17
9
16
10
15
11
14
12
13
VCC
A8
A9
WE
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3
ENCAPSULATED DIP
ORDERING INFORMATION
PART
DS1742-70
DS1742-70+
DS1742-100
DS1742-100+
DS1742-100IND
DS1742-100IND+
DS1742W-120
DS1742W-120+
DS1742W-150
DS1742W-150+
DS1742P-100+
VOLTAGE (V)
5.0
5.0
5.0
5.0
5.0
5.0
3.3
3.3
3.3
3.3
5.0
TEMP RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
PIN-PACKAGE
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
24 EDIP (0.740a)
34 PowerCap®*
TOP MARK**
DS1742-070
DS1742+070
DS1742-100
DS1742+100
DS1742-100 IND
DS1742+100 IND
DS1742W-120
DS1742W+120
DS1742W-150
DS1742W+150
DS1742P+100
+Denotes a lead-free/RoHS-compliant device.
*DS9034-PCX, DS9034I-PCX, DS9034-PCX+ required (must be ordered separately).
** The top mark will include a “+” on lead-free devices.
PowerCap is a registered trademark of Dallas Semiconductor.
1 of 15
REV: 060706
DS1742
PIN DESCRIPTION
PIN
1
2
3
4
5
6
7
8
19
22
23
9
10
11
13
14
15
16
17
12
18
20
21
24
NAME
A7
A6
A5
A4
A3
A2
A1
A0
A10
A9
A8
DQ0
DQ1
DQ2
DQ3
DQ4
DQ5
DQ6
DQ7
GND
CE
OE
WE
VCC
FUNCTION
Address Input
Data Input/Output
Ground
Active-Low Chip-Enable Input
Active-Low Output-Enable Input
Active-Low Write-Enable Input
Power-Supply Input
DESCRIPTION
The DS1742 is a full-function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) and 2k x 8
nonvolatile static RAM. User access to all registers within the DS1742 is accomplished with a bytewide
interface as shown in Figure 1. The RTC information and control bits reside in the eight uppermost RAM
locations. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in
24-hour BCD format. Corrections for the day of the month and leap year are made automatically.
The RTC clock registers are double-buffered to avoid access of incorrect data that can occur during clock
update cycles. The double-buffered system also prevents time loss as the timekeeping countdown
continues unabated by access to time register data. The DS1742 also contains its own power-fail circuitry,
which deselects the device when the VCC supply is in an out-of-tolerance condition. This feature prevents
loss of data from unpredictable system operation brought on by low VCC as errant access and update
cycles are avoided.
2 of 15
DS1742
CLOCK OPERATIONS—READING THE CLOCK
While the double-buffered register structure reduces the chance of reading incorrect data, internal updates
to the DS1742 clock registers should be halted before clock data is read to prevent reading of data in
transition. However, halting the internal clock register updating process does not affect clock accuracy.
Updating is halted when a 1 is written into the read bit, bit 6 of the century register, see Table 2. As long
as a 1 remains in that position, updating is halted. After a halt is issued, the registers reflect the count, that
is day, date, and time that was current at the moment the halt command was issued. However, the internal
clock registers of the double-buffered system continue to update so that the clock accuracy is not affected
by the access of data. All of the DS1742 registers are updated simultaneously after the internal clock
register updating process has been re-enabled. Updating is within a second after the read bit is written to
0. The READ bit must be a zero for a minimum of 500ms to ensure the external registers will be updated.
Figure 1. DS1742 BLOCK DIAGRAM
Table 1. TRUTH TABLE
VCC
CE
VIH
VIL
VCC > VPF
VIL
VIL
VSO < VCC < VPF
X
VCC < VSO < VPF
X
OE
WE
X
X
VIL
VIH
X
X
X
VIL
VIH
VIH
X
X
MODE
Deselect
Write
Read
Read
Deselect
Deselect
3 of 15
DQ
High-Z
Data In
Data Out
High-Z
High-Z
High-Z
POWER
Standby
Active
Active
Active
CMOS Standby
Data Retention Mode
DS1742
SETTING THE CLOCK
As shown in Table 2, bit 7 of the century register is the write bit. Setting the write bit to a 1, like the read
bit, halts updates to the DS1742 registers. The user can then load them with the correct day, date and time
data in 24-hour BCD format. Resetting the write bit to a 0 then transfers those values to the actual clock
counters and allows normal operation to resume.
STOPPING AND STARTING THE CLOCK OSCILLATOR
The clock oscillator may be stopped at any time. To increase the shelf life, the oscillator can be turned off
to minimize current drain from the battery. The OSC bit is the MSB (bit 7) of the seconds registers, see
Table 2. Setting it to a 1 stops the oscillator.
FREQUENCY TEST BIT
As shown in Table 2, bit 6 of the day byte is the frequency test bit. When the frequency test bit is set to
logic 1 and the oscillator is running, the LSB of the seconds register will toggle at 512 Hz. When the
seconds register is being read, the DQ0 line will toggle at the 512 Hz frequency as long as conditions for
access remain valid (i.e., CE low, OE low, WE high, and address for seconds register remain valid and
stable).
CLOCK ACCURACY
The DS1742 is guaranteed to keep time accuracy to within ±1 minute per month at 25°C. Dallas
Semiconductor calibrates the RTC at the factory using nonvolatile tuning elements. The DS1742 does not
require additional calibration. For this reason, methods of field clock calibration are not available and not
necessary. Clock accuracy is also affected by the electrical environment and caution should be taken to
place the RTC in the lowest level EMI section of the PCB layout. For additional information refer to
Application Note 58.
Table 2. REGISTER MAP
ADDRESS
B7
B6
7FF
7FE
X
7FD
7FC
7FB
7FA
7F9
7F8
X
BF
X
X
OSC
W
B5
10 Year
DATA
B4
B3
10
Month
X
10 Date
FT
X
X
X
10 Hour
10 Minutes
10 Seconds
R
10 Century
X
X
B2
B1
Year
Month
X
Date
Day
Hour
Minutes
Seconds
Century
OSC = STOP BIT
R = READ BIT
FT = FREQUENCY TEST
W = WRITE BIT
X = SEE NOTE BELOW
BF = BATTERY FLAG
B0
FUNCTION
RANGE
Year
00–99
Month
01–12
Date
Day
Hour
Minutes
Seconds
Control
01–31
01–07
00–23
00–59
00–59
00–39
Note: All indicated “X” bits are not used but must be set to “0” during write cycle to ensure proper clock operation.
4 of 15
DS1742
RETRIEVING DATA FROM RAM OR CLOCK
The DS1742 is in the read mode whenever OE (output enable) is low, WE (write enable) is high, and CE
(chip enable) is low. The device architecture allows ripple-through access to any of the address locations
in the NV SRAM. Valid data will be available at the DQ pins within tAA after the last address input is
stable, providing that the CE and OE access times and states are satisfied. If CE or OE access times and
states are not met, valid data will be available at the latter of chip enable access (tCEA) or at output enable
access time (tOEA). The state of the data input/output pins (DQ) is controlled by CE , and OE . If the
outputs are activated before tAA, the data lines are driven to an intermediate state until tAA. If the address
inputs are changed while CE and OE remain valid, output data will remain valid for output data hold
time (tOH) but will then go indeterminate until the next address access.
WRITING DATA TO RAM OR CLOCK
The DS1742 is in the write mode whenever WE and CE are in their active state. The start of a write is
referenced to the latter occurring transition of WE on CE . The addresses must be held valid throughout
the cycle. CE or WE must return inactive for a minimum of tWR prior to the initiation of another read or
write cycle. Data in must be valid tDS prior to the end of write and remain valid for tDH afterward. In a
typical application, the OE signal will be high during a write cycle. However, OE can be active provided
that care is taken with the data bus to avoid bus contention. If OE is low prior to WE transitioning low
the data bus can become active with read data defined by the address inputs. A low transition on WE will
then disable the outputs tWEZ after WE goes active.
DATA RETENTION MODE
The 5V device is fully accessible and data can be written or read only when VCC is greater than VPF.
However, when VCC is below the power fail point, VPF, (point at which write protection occurs) the
internal clock registers and SRAM are blocked from any access. When VCC falls below the battery switch
point VSO (battery supply level), device power is switched from the VCC pin to the backup battery. RTC
operation and SRAM data are maintained from the battery until VCC is returned to nominal levels. The
3.3V device is fully accessible and data can be written or read only when VCC is greater than VPF. When
VCC falls below the power fail point, VPF, access to the device is inhibited. If VPF is less than Vso, the
device power is switched from VCC to the backup supply (VBAT) when VCC drops below VPF. If VPF is
greater than Vso, the device power is switched from VCC to the backup supply (VBAT) when VCC drops
below Vso. RTC operation and SRAM data are maintained from the battery until VCC is returned to
nominal levels.
5 of 15
DS1742
BATTERY LONGEVITY
The DS1742 has a lithium power source that is designed to provide energy for clock activity, and clock
and RAM data retention when the VCC supply is not present. The capability of this internal power supply
is sufficient to power the DS1742 continuously for the life of the equipment in which it is installed. For
specification purposes, the life expectancy is 10 years at 25°C with the internal clock oscillator running in
the absence of VCC power. Each DS1742 is shipped from Dallas Semiconductor with its lithium energy
source disconnected, guaranteeing full energy capacity. When VCC is first applied at a level greater than
VPF, the lithium energy source is enabled for battery backup operation. Actual life expectancy of the
DS1742 will be much longer than 10 years since no lithium battery energy is consumed when VCC is
present.
BATTERY MONITOR
The DS1742 constantly monitors the battery voltage of the internal battery. The Battery Flag bit (bit 7) of
the day register is used to indicate the voltage level range of the battery. This bit is not writable and
should always be a 1 when read. If a 0 is ever present, an exhausted lithium energy source is indicated
and both the contents of the RTC and RAM are questionable.
6 of 15
DS1742
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to Ground……………………………………………..-0.3V to +6.0V
Operating Temperature Range……………………………………………...0°C to +70°C (noncondensing)
Storage Temperature Range………………………………………………………………...-40°C to +85°C
Soldering Temperature (EDIP, leads)..………………………………..+260°C for 10 seconds (See Note 7)
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect
reliability.
OPERATING RANGE
RANGE
Commercial
Industrial
TEMPERATURE
0°C to +70°C (noncondensing)
-40°C to +85°C (noncondensing)
VCC
3.3V ±10% or 5V ±10%
3.3V ±10% or 5V ±10%
RECOMMENDED DC OPERATING CONDITIONS
(Over the operating range)
PARAMETER
Logic 1
VCC = 5V ±10%
Voltage
(All Inputs) VCC = 3.3V ±10%
Logic 0
VCC = 5V ±10%
Voltage (All
VCC = 3.3V ±10%
Inputs)
SYMBOL
MIN
VIH
TYP
MAX
UNITS
NOTES
2.2
VCC + 0.3V
V
1
VIH
2.0
VCC + 0.3V
V
1
VIL
-0.3
+0.8
V
1
VIL
-0.3
+0.6
V
1
DC ELECTRICAL CHARACTERISTICS
(VCC = 5.0V ±10%, Over the operating range.)
PARAMETER
SYMBOL
Active Supply Current
TTL Standby Current ( CE = VIH)
CMOS Standby Current
( CE ≥ VCC - 0.2V)
Input Leakage Current
(Any Input)
Output Leakage Current
(Any Output)
Output Logic 1 Voltage
(IOUT = -1.0mA)
Output Logic 0 Voltage
(IOUT = +2.1mA)
Write Protection Voltage
Battery Switchover Voltage
MIN
TYP
MAX
UNITS
NOTES
ICC
ICC1
15
1
50
3
mA
mA
2, 3
2, 3
ICC2
1
3
mA
2, 3
IIL
-1
+1
µA
IOL
-1
+1
µA
VOH
2.4
1
VOL
VPF
0.4
4.25
VSO
4.50
VBAT
7 of 15
1
V
1
1, 4
DS1742
DC ELECTRICAL CHARACTERISTICS
(VCC = 3.3V ±10%, Over the operating range.)
PARAMETER
SYMBOL MIN
TYP
MAX
UNITS
NOTES
Active Supply Current
ICC
10
30
mA
2, 3
TTL Standby Current ( CE = VIH)
CMOS Standby Current
( CE ³ VCC - 0.2V)
Input Leakage Current (any input)
Output Leakage Current
(Any Output)
Output Logic 1 Voltage
(IOUT = -1.0mA)
Output Logic 0 Voltage
(IOUT =2.1mA)
Write Protection Voltage
ICC1
0.7
2
mA
2, 3
ICC2
0.7
2
mA
2, 3
Battery Switchover Voltage
IIL
-1
+1
mA
IOL
-1
+1
mA
VOH
2.4
1
0.4
VOL
VPF
2.80
2.97
VBAT or
VPF
VSO
1
V
1
V
1, 4
UNITS
NOTES
AC CHARACTERISTICS—READ CYCLE (5V)
(VCC = 5.0V ±10%, Over the operating range.)
70ns ACCESS
PARAMETER
SYMBOL
MIN
MAX
Read Cycle Time
tRC
70
Address Access Time
tAA
70
5
tCEL
CE to DQ Low-Z
tCEA
70
CE Access Time
25
tCEZ
CE Data Off time
tOEL
5
OE to DQ Low-Z
tOEA
35
OE Access Time
tOEZ
25
OE Data Off Time
Output Hold from Address
tOH
5
8 of 15
100ns ACCESS
MIN
MAX
100
100
5
100
35
5
55
35
5
ns
ns
ns
ns
ns
ns
ns
ns
ns
DS1742
AC CHARACTERISTICS—READ CYCLE (3.3V)
(VCC = 3.3V ±10%, Over the operating range.)
120ns ACCESS
PARAMETER
SYMBOL
MIN
MAX
Read Cycle Time
tRC
120
Address Access Time
tAA
120
tCEL
5
CE to DQ Low-Z
tCEA
120
CE Access Time
tCEZ
40
CE Data Off time
tOEL
5
OE to DQ Low-Z
tOEA
100
OE Access Time
35
tOEZ
OE Data Off Time
Output Hold from Address
tOH
5
READ CYCLE TIMING DIAGRAM
9 of 15
150ns ACCESS
MIN
MAX
150
150
5
150
50
5
130
35
5
UNITS
NOTES
ns
ns
ns
ns
ns
ns
ns
ns
ns
5
5
5
5
5
5
5
5
5
DS1742
AC CHARACTERISTICS—WRITE CYCLE (5V)
(VCC = 5.0V ±10%, Over the operating range.)
70ns ACCESS
PARAMETER
SYMBOL
MIN
MAX
Write Cycle Time
tWC
70
Address Access Time
tAS
0
tWEW
50
WE Pulse Width
tCEW
60
CE Pulse Width
Data Setup Time
tDS
30
Data Hold time
tDH
0
Address Hold Time
tAH
5
tWEZ
25
WE Data Off Time
Write Recovery Time
tWR
5
100ns ACCESS
MIN
MAX
100
0
70
75
40
0
5
35
5
UNITS NOTES
ns
ns
ns
ns
ns
ns
ns
ns
ns
AC CHARACTERISTICS—WRITE CYCLE (3.3V)
(VCC = 3.3V ±10%, Over the operating range.)
120ns ACCESS
PARAMETER
SYMBOL
MIN
MAX
Write Cycle Time
tWC
120
Address Setup Time
tAS
0
100
tWEW
WE Pulse Width
tCEW
110
CE Pulse Width
Data Setup Time
tDS
80
Data Hold Time
tDH
0
Address Hold Time
tAH
0
40
tWEZ
WE Data Off Time
Write Recovery Time
tWR
10
10 of 15
150ns ACCESS
MIN
MAX
150
0
130
140
90
0
0
50
10
UNITS NOTES
ns
ns
ns
ns
ns
ns
ns
ns
ns
DS1742
WRITE CYCLE TIMING DIAGRAM—WRITE-ENABLE CONTROLLED
WRITE CYCLE TIMING DIAGRAM—CHIP-ENABLE CONTROLLED
11 of 15
DS1742
POWER-UP/POWER-DOWN CHARACTERISTICS (5V)
(VCC = 5.0V ±10%, Over the operating range.)
PARAMETER
SYMBOL
MIN
tPD
0
ms
VCC Fall Time: VPF(MAX) to VPF(MIN)
tF
300
ms
VCC Fall Time: VPF(MIN) to VSO
tFB
10
ms
VCC Rise Time: VPF(MIN) to VPF(MAX)
tR
0
ms
CE
or WE at VIH, Before Power-Down
Power-Up Recover Time
Expected Data Retention Time
(Oscillator On)
tREC
tDR
TYP
MAX
35
10
POWER-UP/POWER-DOWN WAVEFORM TIMING (5V DEVICE)
12 of 15
UNITS
NOTES
ms
years
5, 6
DS1742
POWER-UP/POWER-DOWN CHARACTERISTICS (3.3V)
(VCC = 3.3V ±10%, Over the operating range.)
PARAMETER
SYMBOL
MIN
tPD
0
ms
VCC Fall Time: VPF(MAX) to VPF(MIN)
tF
300
ms
VCC Rise Time: VPF(MIN) to VPF(MAX)
tR
0
ms
CE
or WE at VIH, Before Power-Down
Power-Up Recovery Time
tREC
Expected Data Retention Time
(Oscillator On)
tDR
TYP
MAX
35
10
UNITS
NOTES
ms
years
5, 6
POWER-UP/POWER-DOWN WAVEFORM TIMING (3.3V DEVICE)
CAPACITANCE
(TA = +25°C)
PARAMETER
Capacitance on All Input Pins
Capacitance on All Output Pins
SYMBOL
CIN
CO
MIN
13 of 15
TYP
MAX
7
10
UNITS
pF
pF
NOTES
DS1742
AC TEST CONDITIONS
Output Load: 100pF + 1TTL Gate
Input Pulse Levels: 0.0 to 3.0V
Timing Measurement Reference Levels:
Input: 1.5V
Output: 1.5V
Input Pulse Rise and Fall Times: 5ns
NOTES:
1) Voltage referenced to ground.
2) Typical values are at 25°C and nominal supplies.
3) Outputs are open.
4) Battery switchover occurs at the lower of either the battery voltage or VPF.
5) Data retention time is at 25°C.
6) Each DS1742 has a built-in switch that disconnects the lithium source until VCC is first applied by the
user. The expected tDR is defined as a cumulative time in the absence of VCC starting from the time
power is first applied by the user.
7) Real-time clock modules can be successfully processed through conventional wave-soldering
techniques as long as temperature exposure to the lithium energy source contained within does not
exceed +85°C. Post-solder cleaning with water washing techniques is acceptable, provided that
ultrasonic vibration is not used to prevent damage to the crystal.
14 of 15
DS1742
PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package
outline information, go to www.maxim-ic.com/DallasPackInfo.)
DS1742 24-PIN PACKAGE
15 of 15
Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product.
No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2006 Maxim Integrated Products • Printed USA
The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corporation.