DS1904L-F5# Maxim Integrated Products, DS1904L-F5# Datasheet - Page 2

• Manufacturer Part Number: DS1904L-F5#
• Description: IBUTTON RTC F5 MICROCAN
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1904L-F5#

• Rohs Information: IButton RoHS Compliance Plan
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Memory Size: -
• Memory Type: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

DS1904
hazards such as dirt, moisture, and shock. Accessories permit the DS1904 to be mounted on almost any
surface including printed circuit boards and plastic key fobs. The DS1904 adds functions such as
calendar, time and date stamp, stopwatch, hour meter, interval timer, and logbook to any type of
electronic device or embedded application that uses a microcontroller.
OVERVIEW
The DS1904 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 a 32.768 kHz crystal.
The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide
one of four ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM.
The protocol for these ROM functions is described in Figure 7. After a ROM function command is
successfully executed, the real-time clock functions become accessible and the master may then provide
one of the real-time clock function commands. The protocol for these commands is described in Figure 5.
All data is read and written least significant bit first.
BLOCK DIAGRAM Figure 1
ROM
64-BIT
LID
DATA
FUNCTION
LASERED
CONTACT
CONTROL
ROM
CLOCK
FUNCTION
CONTROL
READ/WRITE BUFFER
3V
1 Hz
RTC COUNTER (32-BIT)
LITHIUM
32.768 kHz
OSCILLATOR
DIVIDER
CONTROL
OSCILLATOR
64-BIT LASERED ROM
Each DS1904 contains a unique ROM code that is 64 bits long. The first eight bits are a 1-Wire family
code. The next 48 bits are a unique serial number. The last eight bits are a CRC of the first 56 bits. (See
Figure 3.) The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and
8
5
4
XOR gates as shown in Figure 4. The polynomial is X
+ X
+ X
+ 1. Additional information about the
Dallas Semiconductor 1-Wire Cyclic Redundancy Check is available in the Book of DS19xx iButton
Standards. The shift register bits are initialized to zero. Then starting with the least significant bit of the
family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the
serial number is entered. After the 48th bit of the serial number has been entered, the shift register
contains the CRC value. Shifting in the eight bits of CRC should return the shift register to all zeros. The
64-bit ROM and ROM Function Control section allow the DS1904 to operate as a 1-Wire device and
follow the 1-Wire protocol detailed in the section "1-Wire Bus System".
2 of 13