Dallas DS1395 Ramified real time clock Datasheet

DS1395/DS1397
DS1395/DS1397
RAMified Real Time Clock
FEATURES
PIN ASSIGNMENT
• Ideal for EISA bus PCs
• Functionally compatible
1
2
28
27
A2
X2
X1
STBY
3
4
26
25
VDD
SQW
5
24
A4
D0
23
A5
D1
6
7
22
D2
8
21
VBAT
IRQ
D3
D4
9
20
RESET
10
19
D6
11
12
18
17
A0
with MC146818 in 32 KHz
mode
• Totally nonvolatile with over 10 years of operation in
the absence of power
• Self-contained
subsystem includes lithium, quartz,
and support circuitry
A1
A3
seconds, minutes, hours, day of the week,
date, month, and year with leap year compensation
D5
D7
13
• Binary or BCD representations of time, calendar, and
16
RD
BGND
WR
XRAM
VSS
14
15
RTC
• Counts
alarm
DS1395S 28-Pin SOIC (330 mil)
• 12- or 24-hour clock with AM and PM in 12-hour mode
• Daylight Savings Time option
• Interfaced with software as 64 register/RAM locations
plus 4K x 8 of static RAM
– 14 bytes of clock and control registers
– 50 bytes of general and control registers
– Separate 4K x 8 nonvolatile SRAM
• Programmable square wave output signal
• Bus-compatible interrupt signals (IRQ)
• Three
interrupts are separately software-maskable
and testable:
– Time-of-day alarm once/second to once/day
– Periodic rates from 122 µs to 500 ms
– End-of-clock update cycle
• 28-pin JEDEC footprint
• Available as chip (DS1395/DS1395S) or stand alone
module with embedded lithium battery and crystal
(DS1397)
ORDERING INFORMATION
DS1395
DS1395S
DS1397
RTC Chip; 28–pin DIP
RTC Chip; 28–pin SOIC
RTC Module; 28–pin DIP
A0
1
28
A2
A1
2
27
A3
X2
3
26
VDD
X1
4
25
SQW
STBY
5
24
A4
D0
6
23
22
A5
VBAT
D2
D3
8
21
IRQ
9
20
RESET
D4
10
19
D5
D6
D7
11
18
17
RD
BGND
WR
VSS
14
D1
7
12
13
16
XRAM
15
RTC
DS1395 28-Pin DIP (600 mil)
A0
1
28
A2
A1
2
27
A3
NC
3
26
NC
4
VDD
SQW
STBY
D0
5
25
24
6
23
A5
D1
7
22
NC
D2
8
21
IRQ
D3
9
20
RESET
D4
10
19
D5
11
NC
D6
12
18
17
D7
13
16
XRAM
V SS
14
15
RTC
A4
RD
WR
DS1397 28-Pin Encapsulated Package (720 mil)
Copyright 1995 by Dallas Semiconductor Corporation.
All Rights Reserved. For important information regarding
patents and other intellectual property rights, please refer to
Dallas Semiconductor databooks.
020794 1/19
DS1395/DS1397
PIN DESCRIPTIONS
VDD, VSS – Bus operational power is supplied to the part
via these pins. The voltage level present on these pins
should be monitored to transition between operational
power and battery power.
D0-D7 – Data Bus (bidirectional): Data is written into
the device from the data bus if either XRAM or RTC is
asserted during a write cycle at the rising edge of a WR
pulse. Data is read from the device and driven onto the
data bus if either XRAM or RTC is asserted during a
read cycle when the RD signal is low.
A0-A5 – Address Bus (input): Various internal registers of the device are selected by these lines. When
RTC is asserted, A0 selects between the indirect address register and RTC data register. When the XRAM
is asserted, A0-A5 addresses a 32–byte page of RAM.
When A5 is high, the RAM page register is accessible.
When A5 is low, A0-A4 address the 32-byte page of
RAM.
cessible. Registers are selected by the A0 line. Data is
driven onto the data bus when RD is low. Data is received from the bus when WR is pulsed low and then
high.
SQW - Square Wave (output): Frequency selectable
output. Frequency is selected by setting register A bits
RS0-RS3. See Table 2 for frequencies that can be selected.
XRAM - Extended RAM Select (input): When this signal is asserted low, the extended RAM bytes are accessible. The XRAM page register is selected when the A5
address line is high. A 32-byte page of RAM is accessible when A5 is low. A0-A4 select the bytes within the
page of RAM pointed to by the page register. Data is
driven onto the data bus when RD is low. Data is received from the bus when WR is pulsed low and then
high.
RD - Read Strobe (input): Data is read from the selected register and driven onto the data bus by the device when this line is low and either RTC or XRAM is asserted.
IRQ - Interrupt Request (output): The IRQ signal is an
active low, open drain output that is used as a processor
interrupt request. The IRQ output follows the state of
the IRQF bit (bit 7) in status register C. IRQ can be asserted by the alarm, update ended, or periodic interrupt
functions depending on the configuration of register B.
WR - Write Strobe (input): Data is written into the device from the data bus on the rising edge after a low
pulse on this line when the device has been selected by
either the XRAM or RTC signals.
RESET - Reset (input): The reset signal is used to initialize certain registers to allow proper operation of the
RTC module. When RESET is low, the following occurs.
STBY - Standby (input): Accesses to the device are
inhibited and outputs are tri-stated to a high impedance
state when this signal is asserted low. All data in RAM of
the device is preserved. The real time clock continues
to keep time.
1. The following register bits are cleared:
a. Periodic interrupt (PIE)
b. Alarm interrupt enable (AIE)
c. Update ended interrupt (UF)
d. Interrupt request flag (IRQF)
If a read or write cycle is in progress when the STBY signal is asserted low, the internal cycle will be terminated
when either the external cycle completes or when the internal chip enable condition (VDD is 4.25 volts, typical) is
negated, whichever occurs first.
e. Periodic interrupt flag (PF)
f. Alarm interrupt flag (AF)
g. Square wave output enable (SQWE)
h. Update ended interrupt enable (UIE)
2. The IRQ pin is in the high impedance state.
RTC - Real Time Clock Select (input): When this signal is asserted low, the real time clock registers are ac-
020794 2/19
3. The RTC is not processor accessible.
DS1395/DS1397
ADDITIONAL PIN DESCRIPTION
(FOR DS1395, DS1395S)
X1, X2 – Connections for a standard 32.768 KHz quartz
crystal, Daiwa part number DT-26S or equivalent. The
internal oscillator circuitry is designed for operation with
a crystal having a specified load capacitance (CL) of
6 pF. The crystal is connected directly to the X1 and X2
pins. There is no need for external capacitors or resistors. Note: X1 and X2 are very high impedance nodes.
It is recommended that they and the crystal be guard–
ringed with ground and that high frequency signals be
kept away from the crystal area. For more information
on crystal selection and crystal layout considerations,
please consult Application Note 58, “Crystal Considerations with Dallas Real Time Clocks”.
VBAT – Battery input for any standard +3 volt lithium cell
or other energy source. Battery voltage must be held
between 2.5 and 3.5 volts for proper operation. The
nominal write protect trip point voltage at which access
to the real time clock and user RAM is denied is set by
the internal circuitry as 1.26 x VBAT. A maximum load of
1 µA at 25oC and 3.0V on VBAT in the absence of power
should be used to size the external energy source.
The battery should be connected directly to the VBAT
pin. A diode must not be placed in series with the battery
to the VBAT pin. Furthermore, a diode is not necessary
because reverse charging current protection circuitry is
provided internal to the device and has passed the
requirements of Underwriters Laboratories for UL listing.
BGND – Battery ground: This pin or pin 14 can be used
for the battery ground return.
When VDD falls below the CETHR (4.25 volts typical), the
chip select inputs RTC and XRAM are forced to an inactive state regardless of the state of the pin signals. This
puts the module into a write protected mode in which all
inputs are ignored and all outputs are in a high impedance state. When VDD falls below 3.2 volts (typical), the
module is switched over to an internal power source in
the case of the DS1397, or to an external battery connected to the VBAT and BGND pins in the case of the
DS1395 and DS1395S, so that power is not interrupted
to timekeeping and nonvolatile RAM functions.
Address Map: The registers of the device appear in two
distinct address ranges. One set of registers is active
when RTC is asserted low and represents the real time
clock. The second set of registers is active when XRAM
is asserted low and represents the extended RAM.
RTC Address Map: The address map of the RTC module is shown in Figure 2. The address map consists of
50 bytes of general purpose RAM, 10 bytes of RTC/calendar information, and 4 bytes of status and control information. All 64 bytes can be accessed as read/write
registers except for the following:
1. Registers C and D are Read Only (status information)
2. Bit 7 of register A is Read Only
3. Bit 7 of the ”Seconds” byte (00) is Read Only
The first byte of the real time clock address map is the
RTC indirect address register, accessible when A0 is
low. The second byte is the RTC data register, accessible when A0 is high. The function of the RTC indirect address register is to point to one of the 64 RTC registers
that are indirectly accessible through the RTC data register.
OPERATION
Power-Down/Power-Up: The real time clock will continue to operate and all of the RAM, time, and calendar
and alarm memory locations will remain non-volatile regardless of the voltage level of VDD. When the voltage
level applied to the VDD input is greater than 4.25 volts
(typical), the module becomes accessible after 200 ms
provided that the oscillator and countdown chain have
been programmed to be running. This time period allows the module to stabilize after power is applied.
Extended RAM Address Map: The first 32 bytes of the
extended RAM represent one of 128 pages of general
purpose nonvolatile memory. These 32 bytes on a page
are addressed by A0 through A4 when A5 is low. When
A5 is high, the XRAM page register is accessible. The
value in the XRAM page register points to one of 128
pages of nonvolatile memory available. The address of
the XRAM page register is dependent only on A5 being
high; thus, there are 31 aliases of this register in I/0
spaces. (See Figure 3.)
020794 3/19
DS1395/DS1397
TIME, CALENDAR AND ALARM LOCATIONS
The time and calendar information is obtained by reading the appropriate register bytes shown in Table 1. The
time, calendar, and alarm are set or initialized by writing
the appropriate register bytes. The contents of the time,
calendar, and alarm registers can be either Binary or
Binary-Coded Decimal (BCD) format. Table 1 shows
the binary and BCD formats of the twelve time, calendar,
and alarm locations.
Before writing the internal time, calendar, and alarm registers, the SET bit in Register B should be written to a
logic one to prevent updates from occurring while access is being attempted. Also at this time, the data format (binary or BCD), should be set via the data mode bit
(DM) of Register B. All time, calendar, and alarm registers must use the same data mode. The set bit in Register B should be cleared after the data mode bit has been
written to allow the real-time clock to update the time
and calendar bytes.
Once initialized, the real-time clock makes all updates in
the selected mode. The data mode cannot be changed
without reinitializing the ten data bytes. The 24/12 bit
cannot be changed without reinitializing the hour locations. When the 12-hour format is selected, the high or-
020794 4/19
der bit of the hours byte represents PM when it is a logic
one. The time, calendar, and alarm bytes are always accessible because they are double buffered. Once per
second the ten bytes are advanced by one second and
checked for an alarm condition. If a read of the time and
calendar data occurs during an update, a problem exists
where seconds, minutes, hours, etc. may not correlate.
The probability of reading incorrect time and calendar
data is low. Several methods of avoiding any possible
incorrect time and calendar reads are covered later in
this text.
The three alarm bytes can be used in two ways. First,
when the alarm time is written in the appropriate hours,
minutes, and seconds alarm locations, the alarm interrupt is initiated at the specified time each day if the alarm
enable bit is high . The second method is to insert a
“don’t care” state in one or more of the three alarm bytes.
The “don’t care” code is any hexadecimal value from C0
to FF. The two most significant bits of each byte set the
“don’t care” condition when at logic 1. An alarm will be
generated each hour when the “don’t care” bits are set in
the hours byte. Similarly, an alarm is generated every
minute with “don’t care” codes in the hours and minute
alarm bytes. The “don’t care” codes in all three alarm
bytes create an interrupt every second.
V BAT
XRAM
RTC
A0–A5
WR
RD
D0–D7
STBY
VDD
CE
PCK
BUS
INTERFACE
POWER
SWITCHING
REFERENCE
A0–A3
A4–A11
DATA/CONTROL
VPP
ON/OFF
÷8
RST
÷64
RST
÷ 64
RS0–RS3
4
3
3
10
RST
ROW DECODER, 1 OF 256
EXTENDED RAM
4096 BYTES
COLUMN DECODER, 1 OF 16
EXTENDED RAM PAGE REGISTER
ROW DECODER, 1 OF 8
50 BYTES USER RAM
COLUMN DECODER 1 OF 8
CLOCK CALENDAR
AND ALARM
REGISTERS
REGISTERS
A,B,C,D
PERIODIC INTR/SQ WAVE SELECTOR
INDEX
REGISTER
OSC
KHz
DECODER
32.768
÷2
CLOCK
CALENDAR
UPDATE
SQ WAVE
OUT
IRQ
RST
SQW
DS1395/DS1397
DS139X BLOCK DIAGRAM Figure 1
020794 5/19
DS1395/DS1397
REAL TIME CLOCK RAM MAP Figure 2
RTC
RTC +1
INDIRECT ADDRESS REGISTER
RTC DATA REGISTER
14– BYTES
REAL TIME CLOCK
INDIRECT
ADDRESS
00
00
14–BYTES
RTC
00
SECONDS
01
SECONDS ALARM
02
MINUTES
03
MINUTES ALARM
04
HOURS
05
HOURS ALARM
06
DAY OF WEEK
07
DAY OF MONTH
08
MONTH
09
YEAR
0A
REGISTER A
0B
REGISTER B
0C
REGISTER C
0D
REGISTER D
0D
13
14
0E
50–BYTES
USER RAM
3F
63
EXTENDED RAM ADDRESS MAP Figure 3
XRAM
THRU
128 PAGES
OF 32–BYTES
EXTENDED RAM
01
PAGE 00
XRAM + 1F
XRAM + 20
XRAM PAGE REGISTER
XRAM + 21
THRU
XRAM + 3F
020794 6/19
PAGE 7F
02
ALIASES OF
PAGE REGISTER
DS1395/DS1397
TIME, CALENDAR AND ALARM DATA MODES Table 1
ADDRESS
LOCATION
FUNCTION
DECIMAL
RANGE
RANGE
BINARY DATA MODE
BCD DATA MODE
0
Seconds
0-59
00-3B
00-59
1
Seconds Alarm
0-59
00-3B
00-59
2
Minutes
0-59
00-3B
00-59
3
Minutes Alarm
0-59
00-3B
00-59
4
Hours-12-hr Mode
1-12
01-0C AM, 81-8C PM
01-12AM,81-92PM
Hours-24-hr Mode
0-23
00-17
00-23
Hours Alarm-12-hr
1-12
01-0C AM, 81-8C PM
01-12AM,81-92PM
Hours Alarm-24-hr
0-23
00-17
00-23
6
Day of the Week
Sunday = 1
1-7
01-07
01-07
7
Date of the Month
1-31
01-1F
01-31
8
Month
1-12
01-0C
01-12
9
Year
0-99
00-63
00-99
5
USER NONVOLATILE RAM - RTC
The 50 user nonvolatile RAM bytes are not dedicated to
any special function within the DS1395/DS1397. They
can be used by the application program as nonvolatile
memory and are fully available during the update cycle.
This memory is directly accessible in the RTC section.
INTERRUPTS
The RTC plus RAM includes three separate, fully automatic sources of interrupt for a processor. The alarm interrupt can be programmed to occur at rates from once
per second to once per day. The periodic interrupt can
be selected for rates from 500 ms to 122 µs. The update-ended interrupt can be used to indicate to the program that an update cycle is complete. Each of these
independent interrupt conditions is described in greater
detail in other sections of this text.
The application program can select which interrupts, if
any, are going to be used. Three bits in Register B enable the interrupts. Writing a logic 1 to an interrupt-enable bit permits that interrupt to be initiated when the
event occurs. A logic 0 in an interrupt-enable bit prohibits the IRQ pin from being asserted from that interrupt
condition. If an interrupt flag is already set when an interrupt is enabled, IRQ is immediately set at an active
level, although the interrupt initiating the event may
have occurred much earlier. As a result, there are cases
where the program should clear such earlier initiated interrupts before first enabling new interrupts.
When an interrupt event occurs, the relating flag bit is
set to logic 1 in Register C. These flag bits are set independent of the state of the corresponding enable bit in
Register B. The flag bit can be used in a polling mode
without enabling the corresponding enable bits. When a
flag is set, an indication is given to software that an interrupt event has occurred since the flag bit was last read.
However, care should be taken when using the flag bits
as they are cleared each time Register C is read.
Double latching is included with Register C so that bits
which are set remain stable throughout the read cycle.
All bits which are set (high) are cleared when read and
new interrupts which are pending during the read cycle
are held until after the cycle is completed. One, two, or
three bits can be set when reading Register C. Each utilized flag bit should be examined when read to ensure
that no interrupts are lost.
The alternative flag bit usage method is with fully enabled interrupts. When an interrupt flag bit is set and the
corresponding interrupt enable bit is also set, the IRQ
pin is asserted low. IRQ is asserted as long as at least
one of the three interrupt sources has its flag and enable
bits both set. The IRQF bit in Register C is a one whenever the IRQ pin is being driven low. Determination that
020794 7/19
DS1395/DS1397
the RTC initiated an interrupt is accomplished by reading Register C. A logic one in bit 7 (IRQF bit) indicates
that one or more interrupts have been initiated by the
DS1395/DS1397. The act of reading Register C clears
all active flag bits and the IRQF bit.
wave output frequency. These frequencies are listed in
Table 2. The SQW frequency selection shares its
1-of-15 selector with the periodic interrupt generator.
Once the frequency is selected, the output of the SQW
pin can be turned on and off under program control with
the square wave enable bit (SQWE).
OSCILLATOR CONTROL BITS
When the DS1395/DS1397 is shipped from the factory,
the internal oscillator is turned off. This feature prevents
the lithium battery from being used until it is installed in a
system. A pattern of 010 in bits 4 through 6 of Register A
will turn the oscillator on and enable the countdown
chain. A pattern of 11X will turn the oscillator on, but
holds the countdown chain of the oscillator in reset. All
other combinations of bits 4 through 6 keep the oscillator off.
SQUARE WAVE OUTPUT SELECTION
Thirteen of the 15 divider taps are made available to a
1-of-15 selector, as shown in the block diagram of Figure 1. The first purpose of selecting a divider tap is to
generate a square wave output signal on the SQW pin.
The RS0-RS3 bits in Register A establish the square
PERIODIC INTERRUPT SELECTION
The periodic interrupt will cause the IRQ pin to go to an
active state from once every 500 ms to once every
122 µs. This function is separate from the alarm interrupt which can be output from once per second to once
per day. The periodic interrupt rate is selected using the
same Register A bits which select the square wave frequency (see Table 1). Changing the Register A bits affects both the square wave frequency and the periodic
interrupt output. However, each function has a separate
enable bit in Register B. The SQWE bit controls the
square wave output. Similarly, the periodic interrupt is
enabled by the PIE bit in Register B. The periodic interrupt can be used with software counters to measure inputs, create output intervals, or await the next needed
software function.
PERIODIC INTERRUPT RATE AND SQUARE WAVE OUTPUT FREQUENCY Table 2
SELECT BITS REGISTER A
tPI PERIODIC
INTERRUPT RATE
SQW OUTPUT
FREQUENCY
RS3
RS2
RS1
RS0
0
0
0
0
None
None
0
0
0
1
3.90625 ms
256 Hz
0
0
1
0
7.8125 ms
128 Hz
0
0
1
1
122.070 µs
8.192 KHz
0
1
0
0
244.141 µs
4.096 KHz
0
1
0
1
488.281 µs
2.048 KHz
0
1
1
0
976.5625 µs
1.024 KHz
0
1
1
1
1.953125 ms
512 Hz
1
0
0
0
3.90625 ms
256 Hz
1
0
0
1
7.8125 ms
128 Hz
1
0
1
0
15.625 ms
64 Hz
1
0
1
1
31.25 ms
32 Hz
1
1
0
0
62.5 ms
16 Hz
1
1
0
1
125 ms
8 Hz
1
1
1
0
250 ms
4 Hz
1
1
1
1
500 ms
2 Hz
020794 8/19
DS1395/DS1397
UPDATE CYCLE
The DS1395/DS1397 executes an update cycle once
per second regardless of the SET bit in Register B.
When the SET bit in Register B is set to one, the user
copy of the double buffered time, calendar, and alarm
bytes is frozen and will not update as the time increments. However, the time countdown chain continues
to update the internal copy of the buffer. This feature allows time to maintain accuracy independent of reading
or writing the time, calendar, and alarm buffers and also
guarantees that time and calendar information is consistent. The update cycle also compares each alarm
byte with the corresponding time byte and issues an
alarm if a match or if a “don’t care” code is present in all
three positions.
There are three methods that can handle access of the
real-time clock that avoid any possibility of accessing inconsistent time and calendar data. The first method
uses the update-ended interrupt. If enabled, an interrupt occurs after every update cycle that indicates that
over 999 ms are available to read valid time and date information. If this interrupt is used, the IRQF bit in Regis-
ter C should be cleared before leaving the interrupt routine.
A second method uses the update-in-progress bit (UIP)
in Register A to determine if the update cycle is in progress. The UIP bit will pulse once per second. After the
UIP bit goes high, the update transfer occurs 244 µs later. If a low is read on the UIP bit, the user has at least
244 µs before the time/calendar data will be changed.
Therefore, the user should avoid interrupt service routines that would cause the time needed to read valid
time/calendar data to exceed 244 µs.
The third method uses a periodic interrupt to determine
if an update cycle is in progress. The UIP bit in Register
A is set high between the setting of the PF bit in Register
C (see Figure 3). Periodic interrupts that occur at a rate
of greater than tBUC allow valid time and date information to be reached at each occurrence of the periodic interrupt. The reads should be complete within
(tPI/2+tBUC) to ensure that data is not read during the update cycle.
UPDATE-ENDED AND PERIODIC INTERRUPT RELATIONSHIP Figure 4
UIP BIT IN
REGISTER A
t BUC
UF BIT IN
REGISTER C
t PI/2
t PI/2
PF BIT IN
REGISTER C
t
PI
tPI = Periodic interrupt time interval per Table 1.
tBUC = Delay time before update cycle = 244 µs.
020794 9/19
DS1395/DS1397
REGISTERS
The DS1395/DS1397 has four control registers which
are accessible at all times, even during the update
cycle.
REGISTER A
MSB
LSB
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
UIP
DV2
DV1
DV0
RS3
RS2
RS1
RS0
UIP - The Update In Progress (UIP) bit is a status flag
that can be monitored. When the UIP bit is a one, the
update transfer will soon occur. When UIP is a zero, the
update transfer will not occur for at least 244 µs. The
time, calendar, and alarm information in RAM is fully
available for access when the UIP bit is zero. The UIP
bit is read only. Writing the SET bit in Register B to a one
inhibits any update transfer and clears the UIP status
bit.
SET - When the SET bit is a zero, the update transfer
functions normally by advancing the counts once per
second. When the SET bit is written to a one, any update
transfer is inhibited and the program can initialize the
time and calendar bytes without an update occurring in
the midst of initializing. Read cycles can be executed in
a similar manner. SET is a read/write bit that is not modified by internal functions of the DS1395/DS1397.
PIE - The Periodic Interrupt Enable bit is a read/write bit
which allows the Periodic Interrupt Flag (PF) bit in Register C to drive the IRQ pin low. When the PIE bit is set to
one, periodic interrupts are generated by driving the
IRQ pin low at a rate specified by the RS3-RS0 bits of
Register A. A zero in the PIE bit blocks the IRQ output
from being driven by a periodic interrupt, but the Periodic Flag (PF) bit is still set at the periodic rate. PIE is not
modified by any internal DS1395/DS1397 functions but
is cleared by the hardware RESET signal.
DV2, DV1, DV0 - These three bits are used to turn the
oscillator on or off and to reset the countdown chain. A
pattern of 010 is the only combination of bits that will turn
the oscillator on and allow the RTC to keep time. A pattern of 11X will enable the oscillator but holds the countdown chain in reset. The next update will occur at 500
ms after a pattern of 010 is written to DV2, DV1, and
DV0.
AIE - The Alarm Interrupt Enable (AIE) bit is a read/write
bit which, when set to a one, permits the Alarm Flag (AF)
bit in register C to assert IRQ. An alarm interrupt occurs
for each second that the three time bytes equal the three
alarm bytes including a don’t care alarm code of binary
11XXXXXX. When the AIE bit is set to zero, the AF bit
does not initiate the IRQ signal. The internal functions of
the DS1395/DS1397 do not affect the AIE bit but is
cleared by RESET.
RS3, RS2, RS1, RS0 - These four rate-selection bits select one of the 13 taps on the 15-stage divider or disable
the divider output. The tap selected can be used to generate an output square wave (SQW pin) and/or a periodic interrupt. The user can do one of the following
UIE - The Update Ended Interrupt Enable (UIE) bit is a
read/write bit that enables the Update Ended Flag (UF)
bit in Register C to assert IRQ. The SET bit going high or
the RESET pin going low clears the UIE bit.
1. Enable the interrupt with the PIE bit;
2. Enable the SQW output pin with the SQWE bit;
3. Enable both at the same time and the same rate; or
4. Enable neither.
Table 2 lists the periodic interrupt rates and the square
wave frequencies that can be chosen with the RS bits.
REGISTER B
MSB
LSB
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
SET
PIE
AIE
UIE
SQWE
DM
24/12
DSE
020794 10/19
SQWE - When the Square Wave Enable (SQWE) bit is
set to a one, a square wave signal at the frequency set
by the rate-selection bits RS3 through RS0 is driven out
on a SQW pin. When the SQWE bit is set to zero, the
SQW pin is held low. SQWE is a read/write bit and is
cleared by RESET.
DM - The Data Mode (DM) bit indicates whether time
and calendar information is in binary or BCD format.
The DM bit is set by the program to the appropriate format and can be read as required. This bit is not modified
by internal functions. A one in DM signifies binary data
while a zero in DM specifies Binary Coded Decimal
(BCD) data.
DS1395/DS1397
24/12 - The 24/12 control bit establishes the format of
the hours byte. A one indicates the 24-hour mode and a
zero indicates the 12-hour mode. This bit is read/write.
DSE - The Daylight Savings Enable (DSE) bit is a read/
write bit which enables two special updates when DSE
is set to one. On the first Sunday in April the time increments from 1:59:59 AM to 3:00:00 AM. On the last
Sunday in October when the time first reaches 1:59:59
AM it changes to 1:00:00 AM. These special updates do
not occur when the DSE bit is a zero. This bit is not affected by internal functions.
REGISTER C
MSB
LSB
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
IRQF
PF
AF
UF
0
0
0
0
IRQF - The Interrupt Request Flag (IRQF) bit is set to a
one when one or more of the following are true:
PF = PIE = 1
AF = AIE = 1
UF = UIE = 1
i.e., IRQF = (PF • PIE) + (AF • AIE) + (UF
IRQF bit. The PF bit is cleared by a software read of
Register C or by RESET.
AF - A one in the Alarm Interrupt Flag (AF) bit indicates
that the current time has matched the alarm time. If the
AIE bit is also a one, the IRQ pin will go low and a one will
appear in the IRQF bit. A read of Register C or a RESET
will clear AF.
UF - The Update Ended Interrupt Flag (UF) bit is set after each update cycle. When the UIE bit is set to one, the
one in UF causes the IRQF bit to be a one which will assert the IRQ pin. UF is cleared by reading Register C or
by RESET.
BIT 0 THROUGH BIT 3 - These are reserved bits of the
status Register C. These bits always read zero and cannot be written.
REGISTER D
MSB
• UIE)
Any time the IRQF bit is a one, the IRQ pin is driven low.
All flag bits are cleared after Register C is read by the
program or when the RESET pin is low.
PF - The Periodic Interrupt Flag (PF) is a read-only bit
which is set to a one when an edge is detected on the
selected tap of the divider chain. The RS3 through RS0
bits establish the periodic rate. PF is set to a one independent of the state of the PIE bit. When both PF and
PIE are ones, the IRQ signal is active and will set the
LSB
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
VRT
0
0
0
0
0
0
0
VRT - The Valid RAM and Time (VRT) bit is set to the
one state by Dallas Semiconductor Corporation prior to
shipment. This bit is not writable and should always be a
one when read. If a zero is ever present, an exhausted
internal lithium energy source is indicated and both the
contents of the RTC data and RAM data are questionable.
BIT 6 THROUGH BIT 0 - The remaining bits of Register
D are reserved and not usable. They cannot be written
and, when read, they will always read zero.
020794 11/19
DS1395/DS1397
ABSOLUTE MAXIMUM RATINGS*
VDD Pin Potential to Ground Pin
Input Voltage
Power Dissipation
Storage Temperature
-0.3V to +7.0V
VSS – 0.3 to VDD + 0.3V
500 mW
DS1397: –40°C to +70°C
DS1395: –55°C to +125°C
0°C to 70°C
260°C for 10 seconds
Ambient Temperature
Soldering Temperature
* 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.
(0°C to 70°C)
RECOMMENDED DC OPERATING CONDITIONS
CHARACTERISTIC
TEST CONDITION
Supply Voltage
SYM
MIN
MAX
UNITS
VCC
4.5
5.5
V
Input High Voltage
Recognized as a High Signal Over
Recommended VDD and tA Range
VIH
2.2
VDD+
0.3
V
V
Input Low Voltage
Recognized as a Low Signal Over
Recommended VDD and tA Range
VIL
-0.3
0.8
V
VBAT
2.5
3.5
V
Battery Voltage
DC ELECTRICAL CHARACTERISTICS
CHARACTERISTIC
(VDD = 5.0V + 10%, VSS = 0V, tA = 0° C to 70°C)
TEST CONDITION
SYM
MIN
II
MAX
UNIT
+1
µA
Input Leakage
VIL=0V, VIH=VDD
For any Single Pin: D0-7, RD, WR,
A0-5, XRAM, RTC, RESET
Output High Voltage
VDD=5.0V ILOAD =1 mA
VOH
Output Low Voltage
VDD = 5.0V ILOAD = 2 mA
VOL
0.4
V
Power Supply Current
Outputs Unloaded
IDD
50
mA
STBY pin Input Current
STBY=VDD
ISTBY
+500
µA
STBY pin Input Current
STBY=VSS
ISTBY
–1
µA
TEST CONDITION
Reset Pulse Width
Oscillator Startup
V
SYM
MIN
tRWL
5
MAX
UNIT
µs
tRC
1
s
IRQ Release from RD
High
tIRDS
2
µs
IRQ Release from
RESET Low
tIRR
2
µs
020794 12/19
From Software Enable Via DV Bits
2.4
NOTES
(0°C to 70°C; VDD = 4.5V to 5.5V)
AC SWITCHING CHARACTERISTICS
CHARACTERISTIC
NOTES
NOTES
DS1395/DS1397
IRQ RELEASE DELAY
RD
VHIGH
tRWL
RESET
V HIGH
IRQ
tIRR
tIRDS
OSCILLATOR START-UP
tRC
SQW Pin
WR
VHIGH
DV0–2
NOTE:
Timing assumes RS3-0 Bits = 0011, minimum tPI.
020794 13/19
DS1395/DS1397
(0°C to 70°C; VDD = 4.5V to 5.5V)
BUS TIMING
PARAMETER
SYM
MIN
Cycle Time
tCYC
395
PWRWL
200
Pulse Width, RD/WR Low
Signal Rise and Fall Time, RTC,
XRAM, RD, WR
TYP
MAX
UNIT
DC
ns
ns
tR, tF
30
ns
Address Hold Time
tAH
20
ns
Address Setup Time Before RD
tARS
30
ns
Address Setup Time Before WR
tAWS
0
ns
RTC/XRAM Select Setup Time
Before RD
tCRS
30
ns
RTC/XRAM Select Setup Time
Before WR
tCWS
0
ns
RTC/XRAM Select Hold Time After RD or WR
tCH
20
ns
Read Data Hold Time
tDHR
10
Write Data Hold Time
tDHW
0
Output Data Delay Time from RD
tDDR
20
Write Data Setup Time
tDSW
200
100
ns
200
+5 V
1.1KΩ
D.U.T.
50 pF
020794 14/19
ns
ns
OUTPUT LOAD
680Ω
ns
NOTES
DS1395/DS1397
BUS READ/WRITE TIMING
t CYC
VALID
A0-A5
t
t
F
R
RTC
XRAM
t CWS
t
t
t
F
WR
t
CH
R
PWRWL
AWS
t
t
DSW
DATA BUS
WRITE
DATA
D0–D7
AH
t
DHW
VALID
DATA BUS
READ
DATA
D0–D7
VALID
t
CRS
t DDR
RD
t
t
CH
PWRWL
ARS
t
DHR
t
AH
POWER-DOWN/ POWER-UP TIMING
PARAMETER
SYMBOL
CE High to Power Fail
tPF
Recovery at Power Up
tREC
(tA = 25°C)
MIN
TYP
150
MAX
UNITS
0
ns
NOTES
ms
VCC Slew Rate Power Down
tF
4.0 <VCC < 4.5V
300
µs
VCC Slew Rate Power Down
tFB
3.0 <VCC< 4.0V
10
µs
VCC Slew Rate Power Up
tR
4.5V>VCC>4.0V
0
µs
Expected Data Retention
tDR
10
years
NOTE:
CE is chip enabled for access, an internal signal which is defined by (RD + WR) (XRAM + RTC).
020794 15/19
DS1395/DS1397
CAPACITANCE
(tA = 25°C)
PARAMETER
SYMBOL
Input Capacitance
Output Capacitance
MIN
TYP
MAX
UNITS
CIN
12
pF
COUT
12
pF
NOTES
GENERAL INFORMATION
PARAMETER
SYM
MIN
Expected Data Retention @ 25°C
(DS1397 only)
tDR
10
Years
Clock Accuracy for tDR @ 25°C
(DS1397 only)
CQ
±1
Min/Mo
Clock Accuracy Temperature Coefficient (DS1397)
K
Clock Temperature Coefficient
Turnover Temperature (DS1397
only)
tO
Chip Enable Threshold (DS1397
only)
CETHR
20
TYP
MAX
UNIT
.050
ppm/°C2
30
0°C
4.5
V
POWER–UP CONDITION
CE
VIH
tREC
4.5V
4.25V
4.0V
VCC
tR
POWER FAIL
NOTE:
CE is an internal signal generated by the power switching reference in the DS139X products.
020794 16/19
NOTES
DS1395/DS1397
ÉÉÉÉÉÉ
ÉÉÉÉÉÉ
ÉÉÉÉÉÉ
POWER–DOWN CONDITION
CE
VIH
tPF
tF
VCC
4.5V
4.25V
4.0V
VBAT
tDR
tFB
POWER FAIL
DS1395 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
020794 17/19
DS1395/DS1397
DS1395S 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
020794 18/19
DS1395/DS1397
DS1397 28–PIN 720 MIL FLUSH ENCAPSULATED
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
0.720
18.29
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 3, 4, 18 AND 22 ARE MISSING BY DESIGN.
J
H
B
020794 19/19