Datasheet

MAX31850/MAX31851
Cold-Junction Compensated, 1-Wire
Thermocouple-to-Digital Converters
19Maxim Integrated
Read Scratchpad [BEh]
This command allows the master to read the contents of
Scratchpad. The data transfer starts with the least signifi-
cant bit of byte 0 and continues through the scratchpad
until the 9th byte (byte 8, CRC) is read. The master can
issue a reset to terminate reading at any time if only part
of the scratchpad data is needed. The CRC is computed
while data is read from bytes 0–7, and is shifted out as
byte 8.
Read Power Supply [B4h]
The master device issues this command followed by a read
time slot to determine if any devices on the bus are using
parasite power. During the read time slot, parasite-powered
devices pull the bus low, and externally powered devices
do not pull the bus low. See the Powering the MAX31850/
MAX31851 section for more information.
Building a Cross-Reference Table
The procedure in Figure 9 uses the Search ROM com-
mand to find all MAX31850/MAX31851s 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
initiates all these signals except the presence pulse. All
MAX31850/MAX31851s on the bus are slaves.
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
Figure 9. Building a Cross-Reference Table
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
(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