1024-Bit EEPROM iButton

_______________________________________________________________________________________

5

Detailed 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 into the chip

to provide a guaranteed unique identity for absolute

traceability. Data is transferred serially through 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. Free software for

communication with the DS1972 is available at

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:

64-bit lasered ROM, 64-bit scratchpad, four 32-byte

pages of EEPROM, and a 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: Read

ROM, Match ROM, Search ROM, Skip ROM, Resume,

Overdrive-Skip ROM, or Overdrive-Match ROM. Upon

completion of an Overdrive-Skip ROM or Overdrive-

Match 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

MEMORY

FUNCTION

CONTROL UNIT

DATA MEMORY

4 PAGES OF

256 BITS EACH

CRC-16

GENERATOR

64-BIT

SCRATCHPAD

1-Wire

FUNCTION CONTROL

64-BIT

LASERED ROM

PARASITE POWER

IO

REGISTER PAGE

64 BITS

DS1972

Figure 1. Block Diagram

DS1972 COMMAND LEVEL:

AVAILABLE COMMANDS:

DATA FIELD AFFECTED:

READ ROM

MATCH ROM

SEARCH ROM

SKIP ROM

RESUME

OVERDRIVE-SKIP ROM

OVERDRIVE-MATCH ROM

64-BIT REG. #, RC-FLAG

64-BIT REG. #, RC-FLAG

64-BIT REG. #, RC-FLAG

RC-FLAG

RC-FLAG

RC-FLAG, OD-FLAG

64-BIT REG. #, RC-FLAG, OD-FLAG

1-Wire ROM FUNCTION COMMANDS

(SEE FIGURE 9)

WRITE SCRATCHPAD

READ SCRATCHPAD

COPY SCRATCHPAD

READ MEMORY

64-BIT SCRATCHPAD, FLAGS

64-BIT SCRATCHPAD

DATA MEMORY, REGISTER PAGE

DATA MEMORY, REGISTER PAGE

DS1972-SPECIFIC

MEMORY FUNCTION COMMANDS

(SEE FIGURE 7)

Figure 2. Hierarchical Structure for 1-Wire Protocol