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DS1990A
Serial Number iButton
www.maxim-ic.com
GENERAL DESCRIPTION
The DS1990A Serial Number iButtonO is a rugged data carrier that serves as an electronic registration number for automatic identification. Data is transferred serially through the 1-WireO protocol, which requires only a single data lead and a ground return. Every DS1990A is factory lasered with a guaranteed unique 64-bit registration number that allows for absolute traceability. The durable stainless-steel iButton package is highly resistant to environmental hazards such as dirt, moisture, and shock. Its compact coin-shaped profile is self-aligning with mating receptacles, allowing the DS1990A to be used easily by human operators. Accessories permit the DS1990A iButton to be mounted on almost any object, including containers, pallets, and bags.
SPECIAL FEATURES
Can Be Read in Less Than 5ms Operating Range: 2.8V to 6.0V, -40C to +85C
COMMON iButton FEATURES
Unique Factory-Lasered 64-Bit Registration Number Assures Error-Free Device Selection and Absolute Traceability Because No Two Parts are Alike Built-In Multidrop Controller for 1-Wire Net Digital Identification by Momentary Contact Data can be Accessed While Affixed to Object Economically Communicates to Bus Master with a Single Digital Signal at 16.3kbps Button Shape is Self-Aligning with Cup-Shaped Probes Durable Stainless-Steel Case Engraved with Registration Number Withstands Harsh Environments Easily Affixed with Self-Stick Adhesive Backing, Latched by its Flange, or Locked with a Ring Pressed Onto its Rim Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus: Approved Under Entity Concept for use in Class I, Division 1, Group A, B, C, and D Locations

APPLICATIONS
Access Control Work-In-Progress Tracking Tool Management Inventory Control.
F3 and F5 MicroCAN
F3 size
3.10 0.51
F5 size
5.89 0.51
Branding
ORDERING INFORMATION
a
PART
16.25
TEMP RANGE -40C to +85C -40C to +85C
PACKAGE F5 iButton F3 iButton
89
000000FBC52B
1-Wirea
a
01
DS1990A-F5 DS1990A-F3
17.35
EXAMPLES OF ACCESSORIES
PART DS9096P DS9101 DS9093RA DS9093A DS9092 DESCRIPTION Self-Stick Adhesive Pad Multipurpose Clip Mounting Lock Ring Snap-In Fob iButton Probe
IO
GND
IO
GND
All dimensions are shown in millimeters.
iButton, 1-Wire, and MicroCAN are registered trademarks of Dallas Semiconductor.
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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REV: 033005
DS1990A
PHYSICAL SPECIFICATION
Size Weight DS1990A Safety See mechanical drawing Ca. 2.5 grams th Meets UL#913 (4 Edit.); Intrinsically Safe Apparatus, approval under Entity Concept for use in Class I, Division 1, Group A, B, C, and D Locations.
ABSOLUTE MAXIMUM RATINGS
IO Voltage to GND IO Sink Current Junction Temperature Storage Temperature Range -0.5V, +6.0V 20mA +125C -55C to +125C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to the absolute maximum rating conditions for extended periods may affect device.
ELECTRICAL CHARACTERISTICS
PARAMETER SYMBOL CONDITIONS IO Pin General Data 1-Wire Pullup Resistance RPUP (Notes 1, 2) Input Capacitance CIO (Note 3, 15) Input Load Current IL (Note 4) Input Low Voltage VIL (Notes 1, 5, 6) Input High Voltage VIH (Notes 6, 7) Output-Low Voltage at 4mA VOL (Note 6) Output-High Voltage VOH (Notes 6, 8) Operating Charge QOP (Note 9, 15) Recovery Time tREC (Note 1) Timeslot Duration tSLOT (Note 1) IO Pin, 1-Wire Reset, Presence Detect Cycle Reset Low Time tRSTL (Notes 1, 10) Reset High Time tRSTH (Notes 1, 11) Presence Detect High Time tPDH Presence Detect Low Time tPDL (Note 14) Presence Detect Sample tMSP (Note 1) Time IO Pin, 1-Wire Write Write-0 Low Time tW0L (Note 1) Write-1 Low Time tW1L (Notes 1, 12) IO Pin, 1-Wire Read Read Low Time tRL (Notes 1, 13) Read Sample Time tMSR (Notes 1, 13) (VPUP = 2.8V to 6.0V, TA = -40C to +85C.) MIN TYP MAX UNITS 0.6 100 0.25 2.2 0.4 VPUP 30 1 61 480 480 15 60 60 60 1 1 tRL + d 5 800 0.8 kW pF A V V V V nC s s s s s s s s s s s
60 240 75 120 15 - e 15 - d 15
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DS1990A
Note 1: Note 2: System requirement. Full Rpup range guaranteed by design and simulation, not production tested. Production testing performed at a fixed Rpup value. Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery times. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For more heavily loaded systems, an active pullup such as that found in the DS2480 may be required. Capacitance on the IO pin could be 800pF when power is first applied. If a 5kW resistor is used to pull up the IO line to VPUP, 5s after power has been applied the parasite capacitance will not affect normal communications. Input load is to ground. The voltage on IO needs to be less or equal to VILMAX whenever the master drives the line low. Under certain low voltage conditions, VILMAX may have to be reduced to as much as 0.5V to always guarantee a Presence Pulse. All voltages are referenced to ground. VIH is a function of the internal supply voltage. VPUP = external pullup voltage. 30nC per 72 time slots at 5.0V pullup voltage with a 5kW pullup resistor and tSLOT 120s. The reset low time (tRSTL) should be restricted to a maximum of 960 s, to allow interrupt signaling; a longer duration could mask or conceal interrupt pulses if this device is used in parallel with a DS1994. An additional reset or communication sequence cannot begin until the reset high time has expired. e represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VIH. d represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input-high threshold of the bus master. Presence pulse is guaranteed only after a preceding Reset Pulse (tRSTL). Guaranteed by design, simulation only. Not production tested.
Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15:
DESCRIPTION
The diagram in Figure 1 shows the major function blocks of the device. The DS1990A takes the energy it needs to operate from the IO line, as indicated by the Parasite Power block. The ROM Function Control units includes the 1Wire interface and the logic to implement the ROM function commands, which access 64 bits of lasered ROM.
Figure 1. DS1990A BLOCK DIAGRAM
Parasite Power
IO
ROM Function Control
64-bit Lasered ROM
64-BIT LASERED ROM
Each DS1990A 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 2 for details. The 1Wire CRC is generated using a polynomial generator consisting of a Shift and XOR gates as shown in Figure 3. 8 5 4 The polynomial is X + X + X + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is available in Application Note 27. The Shift register bits are initialized to 0. Then starting with the least significant bit of the family code, one bit at a th time is shifted in. After the 8 bit of the family code has been entered, then the serial number is entered. After the th 48 bit of the serial number has been entered, the Shift register contains the CRC value. Shifting in the 8 bits of CRC returns the Shift register to all 0s.
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DS1990A
Figure 2. 64-BIT LASERED ROM
MSB 8-BIT CRC CODE MSB LSB MSB 48-BIT SERIAL NUMBER LSB LSB 8-BIT FAMILY CODE (01h) MSB LSB
Figure 3. 1-WIRE CRC GENERATOR
POLYNOMIAL = X + X + X + 1
8 5 4
1 STAGE
st
2 STAGE
nd
3 STAGE
rd
4 STAGE
th
5 STAGE
th
6 STAGE
th
7 STAGE
th
8 STAGE
th
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
X
8
INPUT DATA
1-Wire BUS SYSTEM
The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1990A is a slave device. The bus master is typically a microcontroller or PC. For small configurations the 1-Wire communication signals can be generated under software control using a single port pin. Alternatively, the DS2480B 1-Wire line driver chip or serial port adapters based on this chip (DS9097U series) can be used. This simplifies the hardware design and frees the microprocessor from responding in real-time. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The 1-Wire protocol defines bus transactions in terms of the bus state during specific 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 CONFIGURATION
The 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 tri-state outputs. The 1-Wire port of the DS1990A is open-drain with an internal circuit equivalent to that shown in Figure 4. A multi-drop bus consists of a 1-Wire bus with multiple slaves attached. At standard speed the 1-Wire bus has a maximum data rate of 16.3kbps. The value of the pullup resistor primarily depends on the network size and load conditions. For most applications the optimal value of the pullup resistor is approximately 2.2kW. 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 devices on the bus may be reset.
TRANSACTION SEQUENCE
The protocol for accessing the DS1990A through the 1-Wire port is as follows: Initialization ROM Function Command
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DS1990A
Figure 4. HARDWARE CONFIGURATION
SIMPLE BUS MASTER VPUP RPUP RX DATA RX TX 100 W MOSFET DS1990A 1-Wire PORT
TX Open Drain Port Pin
RX = Receive TX = Transmit
DS2480B BUS MASTER +5V HOST CPU Serial Port serial in serial out VDD VPP POL RXD 1-W NC To 1-Wire data
TXD GND DS2480B
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS1990A is on the bus and is ready to operate. For more details, see the 1-Wire Signaling section.
1-Wire ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of ROM function commands that the DS1990A supports. All ROM function commands are 8 bits long. A list of these commands follows (see flowchart in Figure 5).
READ ROM [33h]
This command allows the bus master to read the DS1990A's 8-bit family code, unique 48-bit serial number, and 8bit CRC. This command can only be used if there is a single slave device on the bus. If more than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same time (open drain will produce a wired-AND result). The resultant family code and 48-bit serial number will result in a mismatch of the CRC.
SEARCH ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1-Wire bus or their registration numbers. By taking advantage of the wired-AND property of the bus, the master can use a process of elimination to identify the registration numbers of all slave devices. For each bit of the registration number, starting with the least significant bit, the bus master issues a triplet of time slots. On the first slot, each slave device participating in the search outputs the true value of its registration number bit. On the second slot, each slave device participating in the search outputs the complemented value of its registration number bit. On the third slot, the master writes the true value of the bit to be selected. All slave devices that do not match the bit written by the master stop participating in the search. If both of the read bits are zero, the master knows that slave devices exist with both states of the bit. By choosing which state to write, the bus master branches in the ROM code tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes identify the registration numbers of the remaining devices. Refer to App Note 187: 1-Wire Search Algorithm for a detailed discussion, including an example. 5 of 8
DS1990A
Figure 5. ROM FUNCTIONS FLOW CHART
Bus Master TX Reset Pulse
Bus Master TX ROM Function Command
DS1990A TX Presence Pulse
33h Read ROM Command ? Y
N
F0h Search ROM Command ? Y
N
DS1990A TX Family Code (1 Byte) N
DS1990A TX Bit 0 DS1990A TX Bit 0 Master TX Bit 0 Bit 0 Match ? Y DS1990A TX Bit 1 DS1990A TX Bit 1 Master TX Bit 1 N Bit 1 Match ? Y
DS1990A TX Serial Number (6 Bytes)
DS1990A TX CRC Byte N
DS1990A TX Bit 63 DS1990A TX Bit 63
Master TX Bit 63 Bit 63 Match ? Y
MATCH ROM [55h] / SKIP ROM [CCh]
The minimum set of 1-Wire ROM function commands includes a Match ROM and a Skip ROM command. Since the DS1990A contains only the 64-bit ROM without any additional data fields, Match ROM and Skip ROM are not applicable. The DS1990A will remain silent (inactive) upon receiving a ROM function command that it doesn't support. This allows the DS1990A to coexist on a multidrop bus with other 1-Wire devices that do respond to Match ROM or Skip ROM (example DS1990A and DS1994).
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DS1990A
1-Wire SIGNALING
The DS1990A requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write-Zero, Write-One, and Read-Data. Except for the presence pulse the bus master initiates all these signals. To get from idle to active, the voltage on the 1-Wire line needs to fall from VPUP to below VILMAX. To get from active to idle, the voltage needs to rise from VILMAX to above VIHMIN. The time it takes for the voltage to make this rise, referenced as e in Figure 6, depends on the value of the pullup resistor (RPUP) and capacitance of the 1-Wire network attached. The initialization sequence required to begin any communication with the DS1990A is shown in Figure 6. A Reset Pulse followed by a Presence Pulse indicates the DS1990A is ready to receive a ROM function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line for tRSTL + tF to compensate for the edge.
Figure 6. INITIALIZATION PROCEDURE "RESET AND PRESENCE PULSES"
MASTER TX "RESET PULSE" MASTER RX "PRESENCE PULSE" VPUP VIHMIN VILMAX 0V e tMSP
tF
tRSTL
tPDH MASTER
tPDL tRSTH
tREC DS1990A
RESISTOR
After the bus master has released the line it goes into receive mode (RX). Now the 1-Wire bus is pulled to VPUP via the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the VIHMIN is crossed, the DS1990A waits for tPDH and then transmits a Presence Pulse by pulling the line low for tPDL. To detect a presence pulse, the master must test the logical state of the 1-Wire line at tMSP.
READ/WRITE TIME SLOTS
Data communication with the DS1990A takes place in time slots, which carry a single bit each. Write-time slots transport data from bus master to slave. Read-time slots transfer data from slave to master. The definitions of the write and read-time slots are illustrated in Figure 7. All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below VILMAX, the DS1990A starts its internal timing generator that determines when the data line will be sampled during a write-time slot and how long data will be valid during a read-time slot.
MASTER-TO-SLAVE
For a write-one time slot, the voltage on the data line must have risen above VIHMIN after the write-one low time tW1LMAX is expired. For a write-zero time slot, the voltage on the data line must stay below VILMAX until the write-zero low time tW0LMIN is expired. For most reliable communication the voltage on the data line should not exceed VILMAX during the entire tW0L window. After the voltage has risen above VIHMIN, the DS1990A needs a recovery time tREC before it is ready for the next time slot.
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DS1990A
SLAVE-TO-MASTER
A read-data time slot begins like a write-one time slot. The voltage on the data line must remain below VILMAX until the read low time tRL is expired. During the tRL window, when responding with a 0, the DS1990A will start pulling the data line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again. When responding with a 1, the DS1990A will not hold the data line low at all, and the voltage starts rising as soon as tRL is over. The sum of tRL + d (rise rime) on one side and the internal timing generator of the DS1990A on the other side define the master sampling window (tMSRMIN to tMSRMAX) in which the master must perform a read from the data line. For most reliable communication, tRL should be as short as permissible and the master should read close to but no later than tMSRMAX. After reading from the data line, the master must wait until tSLOT is expired. This guarantees sufficient recovery time tREC for the DS1990A to get ready for the next time slot.
Figure 7. READ/WRITE TIMING DIAGRAM
Write-One Time Slot
VPUP VIHMASTER VIHMIN VILMAX 0V tW1L
tF
e tSLOT RESISTOR MASTER
Write-Zero Time Slot
VPUP VIHMASTER VIHMIN VILMAX 0V tF RESISTOR MASTER tSLOT tW0L
tREC
Read-Data Time Slot
VPUP VIHMASTER VIHMIN VILMAX 0V tRL tMSR Master Sampling Window tF
d
tREC tSLOT
RESISTOR
MASTER
DS1990A
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