Un iButton es ideal para cualquier aplicación donde la información tiene que viajar junto a una persona u objeto. Es útil para la trazabilidad de procesos. Colocado en un llavero, reloj, o un anillo, un iButton puede conceder a su propietario el acceso a un edificio, un PC, una pieza de un equipo, o un vehículo.

Descripción

Características Principales

Características comunes de los Dataloggers iButton

Ds1990A F5

The DS1990A serial number iButton® is a rugged data
carrier that serves as an electronic registration number
for automatic identification. Data is transferred serially
through the 1-Wire® 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 selfaligning with mating receptacles, allowing the DS1990A
to be used easily by human operators. Accessories
enable the DS1990A iButton to be mounted on almost
any object, including containers, pallets, and bags.

Features
♦ Can Be Read in Less Than 5ms
♦ Operating Range: 2.8V to 6.0V, -40°C to +85°C
Common iButton Features
♦ Unique Factory-Lasered 64-Bit Registration
Number Ensures 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

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 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as
shown in Figure 3. The polynomial is X8 + X5 + X4 + 1.
Additional information about the 1-Wire Cyclic
Redundancy Check (CRC) is available in Application
Note 27: Understanding and Using Cyclic Redundancy
Checks with Maxim iButton Products.
The shift register bits are initialized to 0. 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, 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 8
bits of CRC returns the shift register to all 0s.
1-Wire Bus System
The 1-Wire bus is a system that 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 iButton Standards.