DS1972: 1024-Bit EEPROM iButton

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DESCRIPTION

The DS1972 combines 1024 bits of EEPROM, an 8-byte register/control page with up to 7 user read/write bytes,

and a fully-featured 1-Wire interface in a rugged iButton package. Each DS1972 has its own 64-bit ROM

registration number that is factory lasered to provide a guaranteed unique identity for absolute traceability. Data is

transferred serially via the 1-Wire protocol, which requires only a single data contact and a ground return. The

DS1972 has an additional memory area called the scratchpad that acts as a buffer when writing to the main

memory or the register page. Data is first written to the scratchpad from which it can be read back. After the data

has been verified, a Copy Scratchpad command transfers the data to its final memory location. Applications of the

DS1972 include access control/parking meter, Work-In-Progress tracking, tool management, inventory control, and

maintenance/inspection data storage. Software for communication with the DS1972 is available for free download

from the http://www.maxim-ic.com/products/ibutton/ website.

OVERVIEW

The block diagram in Figure 1 shows the relationships between the major control and memory sections of the

DS1972. The DS1972 has four main data components: 1) 64-bit lasered ROM, 2) 64-bit scratchpad, 3) four 32-byte

pages of EEPROM, and 4) 64-bit register page. The hierarchical structure of the 1-Wire protocol is shown in Figure

2. The bus master must first provide one of the seven ROM Function Commands, 1) Read ROM, 2) Match ROM, 3)

Search ROM, 4) Skip ROM, 5) Resume, 6) Overdrive-Skip ROM or 7) Overdrive-Match ROM. Upon completion of

an Overdrive ROM command byte executed at standard speed, the device enters Overdrive mode where all

subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is

described in Figure 9. After a ROM function command is successfully executed, the memory functions become

accessible and the master may provide any one of the four memory function commands. The protocol for these

memory function commands is described in Figure 7. All data is read and written least significant bit first.

Figure 1. Block Diagram

PARASITE POWER

I/O

64-bit

Lasered ROM

1-Wire

Function Control

64-bit

Scratchpad

Data Memory

4 Pages of

256 bits each

CRC16

Generator

Memory

Function

Control Unit

Register Page

64 bits

DS1972