DS1982 Maxim, DS1982 Datasheet - Page 2

• Manufacturer Part Number: DS1982
• Description: The DS1982 1Kb Add-Only iButton is a rugged read/write data carrier that identifies and stores relevant information about the product or person to which it is attached
• Manufacturer: Maxim

DS1982
iButton DESCRIPTION
The DS1982 1Kb Add-Only iButton is a rugged read/write data carrier that identifies and stores relevant
information about the product or person to which it is attached. This information can be accessed with
minimal hardware, for example, a single port pin of a microcontroller. The DS1982 consists of a factory-
lasered registration number that includes a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family
Code (09h) plus 1Kb of EPROM that is user-programmable. The power to program and read the DS1982
is derived entirely from the 1-Wire communication line. Data is transferred serially via the 1-Wire
protocol that requires only a single data lead and a ground return. The entire device can be programmed
and then write-protected if desired. Alternatively, the part may be programmed multiple times with new
data being appended to, but not overwriting, existing data with each subsequent programming of the
device. Note: Individual bits can be changed only from a logical 1 to a logical 0, never from a logical 0 to
a logical 1. A provision is also included for indicating that a certain page or pages of data are no longer
valid and have been replaced with new or updated data that is now residing at an alternate page address.
This page address redirection allows software to patch data and enhance the flexibility of the device as a
standalone database. The 48-bit serial number that is factory-lasered into each DS1982 provides a
guaranteed unique identity that allows for absolute traceability. The durable MicroCan package is highly
resistant to harsh environments such as dirt, moisture, and shock. Its compact button-shaped profile is
self-aligning with cup-shaped receptacles, allowing the DS1982 to be used easily by human operators or
automatic equipment. Accessories permit the DS1982 to be mounted on printed circuit boards, plastic key
fobs, photo-ID badges, ID bracelets, and many other objects. Applications include work-in-progress
tracking, electronic travelers, access control, storage of calibration constants, and debit tokens.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS1982. The DS1982 has three main data components: 1) 64-bit lasered ROM, 2) 1024-bit EPROM,
and 3) EPROM Status Bytes. The device derives its power for read operations entirely from the 1-Wire
communication line by storing energy on an internal capacitor during periods of time when the signal line
is high and continues to operate off of this “parasite” power source during the low times of the 1-Wire
line until it returns high to replenish the parasite (capacitor) supply. During programming, 1-Wire
communication occurs at normal voltage levels and then is pulsed momentarily to the programming
voltage to cause the selected EPROM bits to be programmed. The 1-Wire line must be able to provide 12
volts and 10 milliamperes to adequately program the EPROM portions of the part. Whenever
programming voltages are present on the 1-Wire line a special high voltage detect circuit within the
DS1982 generates an internal logic signal to indicate this condition. The hierarchical structure of the 1-
Wire protocol is shown in Figure 2. The bus master must first provide one of the four ROM function
commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM. These commands operate on
the 64-bit lasered ROM portion of each device and can singulate a specific device if many are present on
the 1-Wire line as well as indicate to the bus master how many and what types of devices are present. The
protocol required for these ROM function commands is described in Figure 9. After a ROM function
command is successfully executed, the memory functions that operate on the EPROM portions of the
DS1982 become accessible and the bus master may issue any one of the five memory function commands
specific to the DS1982 to read or program the various data fields. The protocol for these memory function
commands is described in Figure 6. All data is read and written least significant bit first.
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