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DS2415
1-Wire Time Chip
FEATURESReal-time clock with fully compatible 1-
Wire® MicroLAN interfaceUses the same binary time/date
representation as the DS2404 but with 1
second resolutionClock accuracy ±2 minutes per month at
25°CCommunicates at 16.3kbits per secondUnique, factory-lasered and tested 64-bit
registration number (8-bit family code + 48-
bit serial number + 8-bit CRC tester) assures
absolute traceability because no two parts are
alike8-bit family code specifies device
communication requirements to bus masterBuilt-in multidrop controller ensures
compatibility with other MicroLAN productsOperates over a wide VDD voltage range of
2.5V to 5.5V from -40°C to +85°CLow power, 200nA typically with oscillator
runningCompact, low cost 6-pin TSOC surface
mount package
PIN ASSIGNMENT
PIN DESCRIPTIONPin 1 - GND
Pin 2 - 1-Wire
Pin 3 - VDD
Pin 4 - VBAT
Pin 5 - X1
Pin 6 - X2
ORDERING INFORMATIONDS2415P6-pin TSOC package
DS2415P/T&R Tape & Reel of DS2415P
DS2415X Chip Scale Pkg., Tape &
Reel
DESCRIPTIONThe DS2415 1-Wire time chip offers a simple solution for storing and retrieving vital time information
with minimal hardware. The DS2415 contains a unique, lasered ROM and a real-time clock/calendar
implemented as a binary counter. Only one pin is required for communication with the device. Utilizing a
backup energy source, the data is nonvolatile and allows for stand-alone operation. The DS2415 features
can be used to add functions such as calendar, time and date stamp, and logbook to any type of electronic
device or embedded application that uses a microcontroller.
OVERVIEWThe DS2415 has two main data components: 1) 64-bit lasered ROM, and 2) real-time clock counter
DS2415
1-Wire Time Chip
6-Pin TSOC PACKAGE
TOP VIEW
DS2415
available until the ROM function protocol has been established. This protocol is described in the ROM
functions flow chart (Figure 7). The master must first provide one of four ROM function commands: 1)
Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM. After a ROM function sequence has been
successfully executed, the real-time clock functions are accessible and the master may then provide a real
time clock function command (Figure 5).
DETAILED PIN DESCRIPTION
PINSYMBOLDESCRIPTIONGND
Ground pin.21-Wire
Data input/output. Open drain.3VDD
Internal power line. Connect a capacitor4VBAT
Power input pin. 2.5V to 5.5V.5, 6X1, X2
Crystal pins. Connections for a standard 32.768kHz quartz crystal,EPSON part number C-002RX or C-004R (be sure to request 6pF load
capacitance).
NOTE: X1 and X2 are very high-impedance nodes. It is recommendedthat they and the crystal be guard-ringed with ground and that high
frequency signals be kept away from the crystal area. See Figure 10 and
Application Note 58 for details.
BLOCK DIAGRAM Figure 1
64-BIT LASERED ROMEach DS2415 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.
The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. (See Figure 3.)
The 1-Wire CRC of the lasered ROM is generated using the polynomial X8 + X5 + X4 + 1. Additional
DS2415
The functions required to exercise the control functions of the DS2415 are not accessible until the ROM
function protocol has been satisfied. This protocol is described in the ROM functions flow chart
(Figure 7). The 1-Wire bus master must first provide one of the four ROM function commands. After a
ROM function sequence has been successfully executed, the bus master may then provide one of the
function commands specific to the DS2415 (Figure 5).
HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2
64-BIT LASERED ROM Figure 3 MSB LSB
8-Bit CRC Code48-Bit Serial Number8-Bit Family Code (24H)
MSB LSB MSB LSB MSB LSB
1-WIRE CRC GENERATOR Figure 4Polynomial = X8 + X5 + X4 + 1
DS2415
TIMEKEEPINGA 32.768kHz crystal oscillator is used as the time base for the real-time clock counter. The oscillator can
be turned on or off under software control. The oscillator must be on for the real-time clock to function.
The real-time clock counter is double-buffered. This allows the master to read time without the data
changing while it is being read. To accomplish this, a snapshot of the counter data is transferred to a
read/write buffer, which the user accesses.
DEVICE CONTROL BYTEThe on/off control of the 32.768kHz crystal oscillator is done through the device control byte. This byte
can be read and written through the Clock Function commands.
Device Control Byte6543210U3U2U1
OSCOSC00
Bit 0 - 1 0 No function
Bits 0 and 1 are hard-wired to read all 0s.
Bit 2 - 3 OSC Oscillator Enable/Disable
These bits control/report whether the 32.768kHz crystal oscillator is running. If the oscillator is running,
both OSC bits will read 1. If the oscillator is turned off these bits will read 0. When writing the device
control byte both occurrences of the OSC bit should have identical data. Otherwise, the value in bit
address 3 (bold) takes precedence.
Bit 4 - 7 Un General-purpose user flags
These bits have no particular function within the chip. They can be read and written under the control of
the application software and remain non-volatile as long as there is sufficient voltage at the VDD pin. If
the DS2415 is located inside a battery pack, for example, these bits could convey data on the charging
status from the charging station to the equipment that uses the battery.
Real-Time ClockThe real-time clock is a 32-bit binary counter. It is incremented once per second. The real-time clock can
accumulate 136 years of seconds before rolling over. Time/date is represented by the number of seconds
since a reference point, which is determined by the user. For example, 12:00 a.m., January 1, 1970 could
be a reference point.
CLOCK FUNCTION COMMANDSThe “Clock Function Flow Chart” (Figure 5) describes the protocols necessary for accessing the real-time
clock. With only four bytes of real-time clock and one control byte the DS2415 does not provide random
access. Reading and writing always starts with the device control byte followed by the least significant
byte (LSB) of the time data.
DS2415
READ CLOCK [66h]The Read Clock command is used to read the device control byte and the contents of the real-time clock
counter. After having received the most significant bit of the command code the device copies the actual
contents of the real-time clock counter to the read/write buffer. Now the bus master reads data beginning
with the device control byte followed by the least significant byte through the most significant byte of the
real-time clock. After this the bus master may continue reading from the DS2415. The data received will
be the same as in the first pass through the command flow. The Read Clock command can be ended at
any point by issuing a Reset Pulse.
WRITE CLOCK [99h]The Write Clock command is used to set the real-time clock counter and to write the device control byte.
After issuing the command, the bus master writes first the device control byte, which becomes
immediately effective. After this the bus master sends the least significant byte through the most
significant byte to be written to the real time clock counter. The new time data is copied from the
read/write buffer to the real time clock counter and becomes effective as the bus master generates a Reset
Pulse. If the oscillator is intentionally stopped the real time clock counter behaves as a 4-byte nonvolatile
memory.
DS2415
CLOCK FUNCTION COMMAND FLOW CHART Figure 5
DS2415
HARDWARE CONFIGURATION Figure 6
1-WIRE BUS SYSTEMThe 1-Wire bus is a system that has a single bus master and one or more slaves. In all instances the
DS2415 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware
configuration, transaction sequence, and 1-Wire signaling (signal types and timing). A 1-Wire protocol
defines bus transactions in terms of the bus state during specified time slots that are initiated on the falling
edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter 4 of
the Book of DS19xx iButton Standards.
Hardware ConfigurationThe 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to
drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open
drain or 3-state outputs. The 1-Wire input of the DS2415 is open drain with an internal circuit equivalent
to that shown in Figure 6. A multidrop bus consists of a 1-Wire bus with multiple slaves attached. The 1-
Wire bus has a maximum data rate of 16.3kbits per second and requires a pullup resistor of approximately
5k.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus
must be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low
for more than 120s, one or more of the devices on the bus may be reset. Since the DS2415 gets all its
energy for operation through its VBAT pin it will not perform a power-on reset if the 1-Wire bus is low for
an extended time period.
Transaction SequenceThe protocol for accessing the DS2415 via the 1-Wire port is as follows:InitializationROM Function CommandClock Function Command
