Rainbow Electronics DS2415 User Manual

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1-Wire

DS2415

Time Chip

FEATURES

§ Real-time clock with fully compatible 1-

Wire® MicroLAN interface

§ Uses the same binary time/date

representation as the DS2404 but with 1
second resolution

§ Clock accuracy ±2 minutes per month at

25°C

§ Communicates at 16.3kbits per second

§ Unique, factory-lasered and tested 64-bit

registration number (8-bit family code + 48­bit serial number + 8-bit CRC tester) assures
absolute traceability because no two parts are
alike

§ 8-bit family code specifies device

communication requirements to bus master

§ Built-in multidrop controller ensures

compatibility with other MicroLAN products

§ Operates over a wide VDD voltage range of

2.5V to 5.5V from -40°C to +85°C

§ Low power, 200nA typically with oscillator

running

§ Compact, low cost 6-pin TSOC surface

mount package

PIN ASSIGNMENT

6-Pin TSOC PACKAGE

TOP VIEW

PIN DESCRIPTION

Pin 1 - GND
Pin 2 - 1-Wire
Pin 3 - V
Pin 4 - V
Pin 5 - X1
Pin 6 - X2

DD

BAT

ORDERING INFORMATION

DS2415P 6-pin TSOC package
DS2415P/T&R Tape & Reel of DS2415P
DS2415X Chip Scale Pkg., Tape &

Reel

DESCRIPTION

The 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.

OVERVIEW

The DS2415 has two main data components: 1) 64-bit lasered ROM, and 2) real-time clock counter
(Figure 1). The real-time clock utilizes an on-chip oscillator that is connected to an external 32.768kHz
crystal. All data is read and written least significant bit first. The real-time clock functions will not be

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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

PIN SYMBOL DESCRIPTION

1 GND
21-WireData input/output. Open drain.
3VDDInternal power line. Connect a capacitor
4V

BAT

5, 6 X1, X2

Ground pin.

Power input pin. 2.5V to 5.5V.
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 recommended
that 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 ROM

Each 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
information about the Dallas Semiconductor 1-Wire Cyclic Redundancy Check is available in the Book
of DS19xx iButton Standards
operate as a 1-Wire device and follow the 1-Wire protocol detailed in the section ”1-Wire Bus System.”

®

. The 64-bit ROM and ROM Function Control section allow the DS2415 to

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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 Code 48-Bit Serial Number 8-Bit Family Code (24H)

MSB LSB MSB LSB MSB LSB

1-WIRE CRC GENERATOR Figure 4

Polynomial = X8 + X5 + X4 + 1

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DS2415

TIMEKEEPING

A 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 BYTE

The 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 Byte

76543210

U4 U3 U2 U1

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.

OSC

OSC 0 0

Real-Time Clock

The 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 COMMANDS

The “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.

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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.

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