DS1556P-70 ,1M, Nonvolatile, Y2K-Compliant Timekeeping RAMPIN DESCRIPTION A0–A16 - Address Input DQ0–DQ7 - Data Input/Outputs IRQ/FT - Interrupt, Freque ..
DS1556P-70 ,1M, Nonvolatile, Y2K-Compliant Timekeeping RAMFEATURES PIN CONFIGURATIONS Integrated NV SRAM, Real-Time Clock (RTC), Crystal, Power-Fail Cont ..
DS1556P-70 ,1M, Nonvolatile, Y2K-Compliant Timekeeping RAM DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
DS1556W-120 ,1M, Nonvolatile, Y2K-Compliant Timekeeping RAMFEATURES PIN CONFIGURATIONS Integrated NV SRAM, Real-Time Clock (RTC), Crystal, Power-Fail Cont ..
DS1556WP+120 ,1M, Nonvolatile, Y2K-Compliant Timekeeping RAMPIN DESCRIPTION A0–A16 - Address Input DQ0–DQ7 - Data Input/Outputs IRQ/FT - Interrupt, Freque ..
DS1556WP-120 ,1M, Nonvolatile, Y2K-Compliant Timekeeping RAMPIN DESCRIPTION A0–A16 - Address Input DQ0–DQ7 - Data Input/Outputs IRQ/FT - Interrupt, Freque ..
DTC314TS , Digital transistors (built-in resistor)
DTC314TU , Digital transistors (built-in resistor)
DTC323TS , Digital transistors (built-in resistor)
DTC323-TS , Digital transistors (built-in resistor)
DTC343TS , Digital transistors (built-in resistor)
DTC363EU , Digital transistors (built-in resistors)
DS1556-70+-DS1556WP-120+
1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
FEATURES Integrated NV SRAM, Real-Time Clock
(RTC), Crystal, Power-Fail Control Circuit,
and Lithium Energy Source Clock Registers are Accessed Identically to
the Static RAM; These Registers Reside in
the 16 Top RAM Locations Century Byte Register (i.e., Y2K Compliant) 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%
VCC Power-Supply Tolerance Lithium Energy Source is Electrically
Disconnected to Retain Freshness Until
Power is Applied for the First Time Also Available in Industrial Temperature
Range: -40°C to +85°C
PIN CONFIGURATIONS
DS1556
1M, Nonvolatile, Y2K-Compliant
Timekeeping RAM
RSTVCC
A15
IRQ/FT
WE
A13
A8
A9
A11
OE
A10
CE
DQ7
DQ5
DQ6
DQ4
DQ3
31
A14
DQ1
DQ0
32
30
29
28
27
26
25
24
23
22
21
19
20
A16
A12
DQ2
GND
18
17
Encapsulated DIP
Maxim DS1556
TOP VIEW
IRQ/FT1 2
A15
A16RST
VCC CEDQ7
DQ6DQ5DQ4
DQ3
DQ2
DQ1DQ0
GND5 6 9
10
11 12
13 14
15
16 17
N.C.A1433 32
31 30
29
28 27 26
25
24 23
22
21 20
19 18
A13A12A11
A10A9A8A6A4A2
34 N.C.
X1 GND VBAT X2
PowerCapModule Board (Uses DS9034PCX PowerCap)
Maxim DS1556
19-5500; Rev 9/10
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
PIN DESCRIPTION A0–A16 - Address Input
DQ0–DQ7 - Data Input/Outputs
IRQ/FT - Interrupt, Frequency Test Output (Open Drain)
RST - Power-On Reset Output (Open Drain)
CE - Chip Enable
OE - Output Enable
WE - Write Enable
VCC - Power Supply Input
GND - Ground
N.C. - No Connection
X1, X2 - Crystal Connection
VBAT - Battery Connection
ORDERING INFORMATION
PART TEMP RANGE VOLTAGE
(V) PIN-PACKAGE TOP MARK** DS1556-70+ 0°C to +70°C 5.0 32 EDIP (0.740a) DS1556+070
DS1556-70IND+ -40°C to +85°C 5.0 32 EDIP (0.740a) DS1556+070 IND
DS1556P-70+ 0°C to +70°C 5.0 34 PowerCap* DS1556P+70
DS1556P-70IND+ -40°C to +85°C 5.0 34 PowerCap* DS1556P+70 IND
DS1556W-120+ 0°C to +70°C 3.3 32 EDIP (0.740a) DS1556W+120
DS1556W-120IND+ -40°C to +85°C 3.3 32 EDIP (0.740a) DS1556W+120 IND
DS1556WP-120+ 0°C to +70°C 3.3 34 PowerCap* DS1556WP+120
DS1556WP-120IND+ -40°C to +85°C 3.3 34 PowerCap* DS1556WP+120 IND
+Denotes a lead(Pb)-free/RoHS-compliant package.
*DS9034-PCX+ or DS9034I-PCX+ required (must be ordered separately).
**A “+” in top mark denotes a lead(Pb)-free device. An “IND” anywhere on the top mark indicates an industrial temperature grade device.
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
DESCRIPTION The DS1556 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) with an
RTC alarm, watchdog timer, power-on reset, battery monitor, and 128k x 8 nonvolatile static RAM. User
access to all registers within the DS1556 is accomplished with a byte-wide 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.
The RTC registers are double-buffered into an internal and external set. The user has direct access to the
external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow
the user to access static data. Assuming the internal oscillator is turned on, the internal set of registers is
continuously updated, which occurs regardless of external registers settings to guarantee that accurate
RTC information is always maintained.
The DS1556 has interrupt (IRQ/FT) and reset (RST) outputs which can be used to control CPU activity.
The IRQ/FT interrupt output can be used to generate an external interrupt when the RTC register values
match user programmed alarm values. The interrupt is always available while the device is powered from
the system supply and can be programmed to occur when in the battery-backed state to serve as a system
wake-up. Either the IRQ/FT or RST outputs can also be used as a CPU watchdog timer, CPU activity is
monitored and an interrupt or reset output will be activated if the correct activity is not detected within
programmed limits. The DS1556 power-on reset can be used to detect a system power down or failure
and hold the CPU in a safe reset state until normal power returns and stabilizes; the RST output is used
for this function.
The DS1556 also contains its own power-fail circuitry, which automatically deselects the device when the
VCC supply enters an out of tolerance condition. This feature provides a high degree of data security
during unpredictable system operation brought on by low VCC levels.
PACKAGES The DS1556 is available in two packages (32-pin DIP and 34-pin PowerCap module). The 32-pin DIP
style module integrates the crystal, lithium energy source, and silicon all in one package. The 34-pin
PowerCap module board is designed with contacts for connection to a separate PowerCap (DS9034PCX)
that contains the crystal and battery. This design allows the PowerCap to be mounted on top of the
DS1556P after the completion of the surface mount process. Mounting the PowerCap after the surface
mount process prevents damage to the crystal and battery due to the high temperatures required for solder
reflow. The PowerCap is keyed to prevent reverse insertion. The PowerCap Module board and PowerCap
are ordered separately and shipped in separate containers. The part number for the PowerCap is
DS9034PCX.
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
Figure 1. Block Diagram
Table 1. Operating Modes
VCC CE OE WE
DQ0–DQ7 MODE POWER VIH X X High-Z Deselect Standby
VIL X VIL DIN Write Active
VIL VIL VIH DOUT Read Active VCC > VPF
VIL VIH VIH High-Z Read Active
VSO < VCC
VCC
DATA READ MODE
The DS1556 is in the read mode whenever CE (chip enable) is low and WE (write enable) is high. The
device architecture allows ripple-through access to any valid address location. Valid data will be available
at the DQ pins within tAA after the last address input is stable, providing that CE and OE access times are
satisfied. If CE or OE access times 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.
DATA WRITE MODE
The DS1556 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 or CE. The addresses must be held valid throughout the
Maxim
DS1556
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
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 and 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 internal backup lithium
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 and read only when VCC is greater than VPF.
hen VCC falls below VPF, access to the device is inhibited. If VPF is less than VSO, the device power is
switched from VCC to the internal backup lithium battery when VCC drops below VPF. If VPF is greater
than VSO, the device power is switched from VCC to the internal backup lithium battery when VCC drops
below VSO. RTC operation and SRAM data are maintained from the battery until VCC is returned to
nominal levels.
All control, data, and address signals must be powered down when VCC is powered down.
BATTERY LONGEVITY
The DS1556 has a lithium power source that is designed to provide energy for the 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 DS1556 continuously for the life of the equipment in which it is
installed. For specification purposes, the life expectancy is 10 years at 25C with the internal clock
oscillator running in the absence of VCC. Each DS1556 is shipped from Maxim 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
DS1556 will be much longer than 10 years since no internal battery energy is consumed when VCC is
present.
INTERNAL BATTERY MONITOR
The DS1556 constantly monitors the battery voltage of the internal battery. The Battery Low Flag (BLF)
bit of the Flags Register (B4 of 1FFF0h) is not writable and should always be a 0 when read. If a 1 is ever
present, an exhausted lithium energy source is indicated and both the contents of the RTC and RAM are
questionable.
POWER-ON RESET
A temperature compensated comparator circuit monitors the level of VCC. When VCC falls to the power
fail trip point, the RST signal (open drain) is pulled low. When VCC returns to nominal levels, the RST
signal continues to be pulled low for a period of 40 ms to 200 ms. The power-on reset function is
independent of the RTC oscillator and thus is operational whether or not the oscillator is enabled.
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
CLOCK OPERATIONS
Table 2 and the following paragraphs describe the operation of RTC, alarm, and watchdog functions.
Table 2. Register Map
DATA ADDRESS B7 B6 B5 B4 B3 B2 B1 B0 FUNCTION RANGE
1FFFFh 10 Year Year Year 00-99
1FFFEh X X X 10
Month Month Month 01-12
1FFFDh X X 10 Date Date Date 01-31
1FFFCh X Ft X X X Day Day 01-07
1FFFBh X X 10 Hour Hour Hour 00-23
1FFFAh X 10 Minutes Minutes Minutes 00-59
1FFF9h OSC 10 Seconds Seconds Seconds 00-59
1FFF8h W R 10 Century Century Control 00-39
1FFF7h WDS BMB4 BMB3 BMB2 BMB1 BMB0 RB1 RB0 Watchdog
1FFF6h AE Y ABE Y Y Y Y Y Interrupts
1FFF5h AM4 Y 10 Date Date Alarm Date 01-31
1FFF4h AM3 Y 10 Hours Hours Alarm Hours 00-23
1FFF3h AM2 10 Minutes Minutes Alarm Minutes 00-59
1FFF2h AM1 10 Seconds Seconds Alarm Seconds 00-59
1FFF1h Y Y Y Y Y Y Y Y Unused
1FFF0h WF AF 0 BLF 0 0 0 0 Flags
X = Unused, Read/Writable Under Write and Read Bit Control AE = Alarm Flag Enable
Y = Unused, Read/Writable Without Write and Read Bit Control ABE = Alarm in Battery-Backup Mode Enable
FT = Frequency Test Bit AM1 to AM4 = Alarm Mask Bits
OSC = Oscillator Start/Stop Bit WF = Watchdog Flag
W = Write Bit AF = Alarm Flag
R = Read Bit 0 = 0 (Read Only)
WDS = Watchdog Steering Bit BLF = Battery Low Flag
BMB0 to BMB4 = Watchdog Multiplier Bits RB0 to RB1 = Watchdog Resolution Bits
CLOCK OSCILLATOR CONTROL
The clock oscillator can be stopped at any time. To increase the shelf life of the backup lithium battery
source, the oscillator can be turned off to minimize current drain from the battery. The OSC bit is the
MSB of the Seconds Register (B7 of 1FFF9h). Setting it to a 1 stops the oscillator, setting to a 0 starts the
oscillator. The DS1556 is shipped from Maxim with the clock oscillator turned off, OSC bit set to a 1.
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
READING THE CLOCK
When reading the RTC data, it is recommended to halt updates to the external set of double-buffered RTC
Registers. This puts the external registers into a static state allowing data to be read without register
values changing during the read process. Normal updates to the internal registers continue while in this
state. External updates are halted when a 1 is written into the read bit, B6 of the Control Register
(1FFF8h). As long as a 1 remains in the Control Register read bit, updating is halted. After a halt is
issued, the registers reflect the RTC count (day, date, and time) that was current at the moment the halt
command was issued. Normal updates to the external set of registers will resume within 1 second after the
read bit is set to a 0 for a minimum of 500s. The read bit must be a zero for a minimum of 500s to
ensure the external registers will be updated.
SETTING THE CLOCK
The MSB bit, B7, of the Control Register is the write bit. Setting the write bit to a 1, like the read bit,
halts updates to the DS1556 (1FFF8h to 1FFFFh) registers. After setting the write bit to a 1, RTC
Registers can be loaded with the desired RTC count (day, date, and time) in 24-hour BCD format. Setting
the write bit to a 0 then transfers the values written to the internal RTC Registers and allows normal
operation to resume.
CLOCK ACCURACY (DIP MODULE)
The DS1556 is guaranteed to keep time accuracy to within 1 minute per month at 25C. The RTC is
calibrated at the factory by Maxim using nonvolatile tuning elements, and does not require additional
calibration. For this reason, methods of field clock calibration are not available and not necessary. The
electrical environment also affects clock accuracy, and caution should be taken to place the RTC in the
lowest-level EMI section of the PC board layout. For additional information, refer to Application Note
58.
CLOCK ACCURACY (PowerCap MODULE)
The DS1556 and DS9034PCX are each individually tested for accuracy. Once mounted together, the
module will typically keep time accuracy to within 1.53 minutes per month (35 ppm) at 25°C. The
electrical environment also affects clock accuracy, and caution should be taken to place the RTC in the
lowest-level EMI section of the PC board layout. For additional information, refer to
Application Note 58.
FREQUENCY TEST MODE
The DS1556 frequency test mode uses the open drain IRQ/FT output. With the oscillator running, the
IRQ/FT output will toggle at 512 Hz when the FT bit is a 1, the Alarm Flag Enable bit (AE) is a 0, and
the Watchdog Steering bit (WDS) is a 1 or the Watchdog Register is reset (Register 1FFF7h = 00h). The
IRQ/FT output and the frequency test mode can be used as a measure of the actual frequency of the
32.768 kHz RTC oscillator. The IRQ/FT pin is an open-drain output that requires a pullup resistor for
proper operation. The FT bit is cleared to a 0 on power-up.
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
USING THE CLOCK ALARM
The alarm settings and control for the DS1556 reside within Registers 1FFF2h to 1FFF5h. Register
1FFF6h contains two alarm enable bits: Alarm Enable (AE) and Alarm in Backup Enable (ABE). The AE
and ABE bits must be set as described below for the IRQ/FT output to be activated for a matched alarm
condition.
The alarm can be programmed to activate on a specific day of the month or repeat every day, hour,
minute, or second. It can also be programmed to go off while the DS1556 is in the battery-backed state of
operation to serve as a system wake-up. Alarm mask bits AM1 to AM4 control the alarm mode. Table 3
shows the possible settings. Configurations not listed in the table default to the once per second mode to
notify the user of an incorrect alarm setting.
Table 3. Alarm Mask Bits
AM4 AM3 AM2 AM1 ALARM RATE
1 1 1 1 Once per second
1 1 1 0 When seconds match 1 0 0 When minutes and seconds match
1 0 0 0 When hours, minutes, and seconds match 0 0 0 When date, hours, minutes, and seconds match
When the RTC Register values match Alarm Register settings, the Alarm Flag bit (AF) is set to a 1. If
Alarm Flag Enable (AE) is also set to a 1, the alarm condition activates the IRQ/FT pin. The IRQ/FT
signal is cleared by a read or write to the Flags Register (Address 1FFF0h) as shown in Figure 2 and 3.
When CE is active, the IRQ/FT signal may be cleared by having the address stable for as short as 15 ns
and either OE or WE active, but is not guaranteed to be cleared unless tRC is fulfilled. The alarm flag is
also cleared by a read or write to the Flags Register but the flag will not change states until the end of the
read/write cycle and the IRQ/FT signal has been cleared.
Figure 2. Clearing IRQ Waveforms
CE, 0V
DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
Figure 3. Clearing IRQ Waveforms
The IRQ/FT pin can also be activated in the battery-backed mode. The IRQ/FT will go low if an alarm
occurs and both ABE and AE are set. The ABE and AE bits are cleared during the power-up transition,
however an alarm generated during power-up will set AF. Therefore, the AF bit can be read after system
power-up to determine if an alarm was generated during the power-up sequence. Figure 4 illustrates alarm
timing during the battery-backup mode and power-up states.
Figure 4. Backup Mode Alarm Waveforms
CE=0
