Datasheet

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MAX31826
1-Wire Digital Temperature Sensor
with 1Kb Lockable EEPROM
Figure 9. Building a Cross-Reference Table
Locations 40h–7Fh are now locked. Also, location 81h is
locked with value 55h. Location 81h cannot be changed to
alter the lock status of 40h–7Fh.
Building a Cross-Reference Table
The procedure in Figure 9 uses the Search ROM com-
mand to find all MAX31826s on the 1-Wire bus (16
maximum) and then reads each configuration register to
match the ROM IDs to the hardwired addresses.
1-Wire Signaling
The device uses a strict 1-Wire communication protocol
to ensure data integrity. Several signal types are defined
by this protocol: reset pulse, presence pulse, write-zero,
write-one, read-zero, and read-one. The bus master initi-
ates all these signals except the presence pulse.
Initialization Procedure:
Reset and Presence Pulses
All communication with the device begins with an initial-
ization sequence that consists of a reset pulse from the
master followed by a presence pulse from the device.
This is illustrated in Figure 10. When the device sends the
presence pulse in response to the reset, it is indicating
to the master that it is on the bus and ready to operate.
During the initialization sequence, the bus master trans-
mits (Tx) the reset pulse by pulling the 1-Wire bus low for
480Fs (min). The bus master then releases the bus and
goes into receive mode (Rx). When the bus is released,
the 5kI pullup resistor pulls the 1-Wire bus high. When
the device detects this rising edge, it waits 15Fs to 60Fs
and then transmits a presence pulse by pulling the
1-Wire bus low for 60Fs to 240Fs.
SEARCH ALL
ROM IDs ON BUS
AND
STORE ROM IDs
(F0h COMMAND)
N
MAX
IS THE NUMBER
OF ROM IDs FOUND
DONE
BUILDING CROSS-REFERENCE TABLE
USING ROM IDs AND 4-BIT ADDRESSES
READ SCRATCHPAD 1
(USE AD3−AD0 FROM
CONFIG REGISTER)
MASTER Tx
NEXT ROM ID
INCREMENT COUNTER
N = N + 1
N > N
MAX
?
N
Y
MATCH ROM ID TO
ADDRESS AND ADD TO
CROSS-REFERENCE
TABLE
ROM ID(0) 0000
ROM ID AD3−AD0
CROSS-REFERENCE TABLE
NOTE: TEMPERATURE SENSORS ARE ADDRESSED
BY ROM ID, NOT BY BINARY ADDRESS.
ROM ID(1)
0001
ROM ID(2) 0010
ROM ID(3) 0011
ROM ID(12) 1100
ROM ID(13) 1101
ROM ID(14) 1110
ROM ID(15) 1111