Datasheet
DS1972
1024-Bit EEPROM i
Button
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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
www.maxim-ic.com/ibutton.
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