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DS1904

RTC iButton

SPECIAL FEATURES

 Real-Time Clock/calendar in binary format

 Uses the same binary time/date representation

s the DS1994 but with 1 second resolution

 Clock accuracy is better than ± 2 minutes per

month at 25°C

 Operating temperature range from -40°C to

+85°C

 Over 10 years of operation

COMMON iButton FEATURES

 Unique, 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 alike

 Multidrop controller for MicroLAN

 Digital identification and information by

momentary contact

 Chip-based data carrier compactly stores in-

ormation

 Data can be accessed while affixed to object

 Economically communicates to host with a

single digital signal at 16.3 kbps

 Standard 16 mm diameter and 1-Wire

protocol ensure compatibility with iButton

Device family

 Button shape is self-aligning with cup-shaped

probes

 Durable stainless steel case engraved with

registration number withstands harsh envi-

ronments

 Easily affixed with self-stick adhesive back-

ng, latched by its flange, or locked with a

ring pressed onto its rim

 Presence detector acknowledges when reader

first applies voltage

F5 MicroCan

GND

0.51

5.89

16.25

17.35

40 24

000000FBC52B

1-Wire















All dimensions are shown in millimeters

ORDERING INFORMATION

DS1904L-F5# F5 MicroCan

# Denotes an RoHS-compliant device that may include

lead(Pb) that is exempt under the RoHS requirements.

EXAMPLES OF ACCESSORIES

DS9096P Self-Stick Adhesive Pad

DS9101 Multi-Purpose Clip

DS9093RA Mounting Lock Ring

DS9093A Snap-In Fob

DS9092 iButton Probe

iButton DESCRIPTION

The DS1904 RTC iButton is a rugged real-time clock module that can be accessed with minimal

hardware. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a

1-Wire and i

Button are registered trademarks of Maxim Integrated Products, Inc.

For pricing, delivery, and ordering information, please contact Maxim Direct at

1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

19-4864; Rev 6/13

Summary of content (13 pages)

PAGE 1
DS1904 RTC iButton SPECIAL FEATURES Real-Time Clock/calendar in binary format Uses the same binary time/date representation as the DS1994 but with 1 second resolution Clock accuracy is better than ± 2 minutes per month at 25°C Operating temperature range from -40°C to +85°C Over 10 years of operation Easily affixed with self-stick adhesive backing, latched by its flange, or locked with a ring pressed onto its rim Presence detector acknowledges when reader first applies voltage F5 MicroCan
PAGE 2
DS1904 ground return. The DS1904 contains a unique 64-bit factory-lasered ROM and a real-time clock/calendar implemented as a binary counter. The durable MicroCan package is highly resistant to environmental 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.
PAGE 3
DS1904 HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2 1-Wire Bus Bus Master Other Devices DS1904 Command Level 1-Wire ROM Function Commands (see Figure 7) DS1904 specific Function Commands (see Figure 5) Available Commands Data Fields Affected Read ROM Match ROM Search ROM Skip ROM 64-bit ROM 64-bit ROM 64-bit ROM N/A Write Clock Read Clock RTC Counter, Device Control RTC Counter, Device Control 64-BIT LASERED ROM Figure 3 MSB LSB 8-Bit CRC Code MSB 48-Bit Serial Number LSB MSB 8-Bit
PAGE 4
DS1904 TIMEKEEPING A 32.768 kHz 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.
PAGE 5
DS1904 CLOCK FUNCTION COMMAND FLOW CHART Figure 5 Master TX Control Function Command 66H Read Clock ? Y 99H Write Clock ? Y N DS1904 copies RTC Counter to R/W Buffer N Bus Master TX Device Control Byte Bus Master RX Device Control Byte Bus Master TX LS Byte (7:0) Bus Master RX LS Byte (7:0) Bus Master TX next Byte (15:8) Bus Master RX next Byte (15:8) Bus Master TX next Byte (23:16) Bus Master RX next Byte (23:16) Bus Master TX MS Byte (31:24) Bus Master RX MS Byte (31:24) N N Bus Master TX
PAGE 6
DS1904 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.
PAGE 7
DS1904 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 120 µs, one or more of the devices on the bus may be reset. Since the DS1904 gets all its energy for operation through its VDD pin it will not perform a power-on reset if the 1-Wire bus is low for an extended time period.
PAGE 8
DS1904 ROM FUNCTIONS FLOW CHART Figure 7 Master TX Reset Pulse DS1904 TX Presence Pulse Master TX ROM Function Command 33H Read ROM Command ? Y DS1904 TX Family Code 1 Byte N 55H Match ROM Command ? F0H Search ROM Command ? Y N Y DS1904 TX Bit 0 Master TX Bit 0 DS1904 TX Bit 0 Master TX Bit 0 N Bit 0 Match ? N Bit 0 Match ? Y Y DS1904 TX Serial Number 6 Bytes DS1904 TX Bit 1 Master TX Bit 1 DS1904 TX Bit 1 Master TX Bit 1 N Bit 1 Match ? N Bit 1 Match ? Y Y DS1904 TX Bit 63 DS1904 TX CR
PAGE 9
DS1904 Skip ROM [CCh] This command can save time in a single drop bus system by allowing the bus master to access the clock functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, a read command is issued following the Skip ROM command, data collision will occur on the bus as multiple slaves transmit simultaneously (open drain pull-downs will produce a wired-AND result). 1–WIRE SIGNALING The DS1904 requires strict protocols to ensure data integrity.
PAGE 10
DS1904 READ/WRITE TIMING DIAGRAM Figure 9 Write-one Time Slot tSLOT VPULLUP tREC VPULLUP MIN VIH MIN DS1904 Sampling Window VIL MAX 0V tLOW1 15µs 60µs 60 µs ≤ tSLOT < 120 µs RESISTOR 1 µs ≤ tLOW1 < 15 µs MASTER 1 µs ≤ tREC < ∞ Write-zero Time Slot tREC tSLOT VPULLUP VPULLUP MIN VIH MIN DS1904 Sampling Window VIL MAX 0V 15µs 60µs t LOW0 RESISTOR 60 µs ≤ tLOW0 < tSLOT < 120 µs 1 µs ≤ tREC < ∞ MASTER Read-data Time Slot tREC tSLOT VPULLUP VPULLUP MIN VIH MIN Master Sampling Window VIL MAX 0
PAGE 11
DS1904 PHYSICAL SPECIFICATION Size Weight Expected Service Life See mechanical drawing 3.3 grams See Lifetime Graph ABSOLUTE MAXIMUM RATINGS Voltage Range on 1-Wire to Ground Operating Temperature Range Storage Temperature Range * -0.5V to +7.0V -40°C to +85°C* -40°C to +85°C* Storage or operation above +50°C significantly reduces battery life.
PAGE 12
DS1904 NOTES: 1. All voltages are referenced to ground. 2. VPUP = external pull-up voltage; see Figure 6. 3. Under certain low voltage conditions VIL1MAX may have to be reduced to as much as 0.5V to always guarantee a presence pulse. 4. Input load is to ground. 5. Guaranteed by design; not production tested. 6. The master must read while the data is valid. 7. Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit.
PAGE 13
DS1904 REVISION HISTORY REVISION DESCRIPTION DATE 2/00 Initial release Added # to the Ordering Information to reflect the conversion to a 8/09 RoHS-compliant product. Updated the UL certificate reference in the Common iButton Features and Physical Specification sections; relocated VPUP from the DC 4/11 Electrical Characteristics global header to the table and deleted the VOH parameter; added reference to Figure 6 to the EC table note 2; added the Package Information section.