DS1821
10 of 18
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by a presence pulse transmitted by the
DS1821. The presence pulse lets the bus master know that the DS1821 is on the bus and ready to
operate. Timing for the reset and presence pulses is detailed in the 1-Wire SIGNALING section.
DS1821 FUNCTION COMMANDS
The DS1821 function commands in this section allow the master to communicate with and configure the
DS1821. The DS1821 function commands are summarized in Table 4.
READ TEMPERATURE [AAh]
Provides read access to the 1-byte temperature register.
START CONVERT T [EEh]
Initiates temperature conversions. If the part is in one-shot mode (1SHOT = 1), only one conversion will
be performed. If it is in continuous mode (1SHOT = 0), continuous conversions will be performed until a
Stop Convert T command is received.
STOP CONVERT T [22h]
Stops temperature conversions when the device is in continuous conversion mode (1SHOT = 0). This
opcode has no function if the device is in one-shot mode (1SHOT = 1).
WRITE TH [01h]
WRITE TL [02h]
Provides write access to the 8-bit T
H
and T
L
registers, respectively.
READ TH [A1h]
READ TL [A2h]
Provides read access to the 8-bit T
H
and T
L
registers, respectively.
WRITE STATUS [0Ch]
Provides write access to the 8-bit status/configuration register.
READ STATUS [ACh]
Provides read access to the 8-bit status/configuration register.
READ COUNTER [A0h]
Provides read access to data in the 9-bit counter register for use in high-resolution temperature
calculations. This is explained in detail in the HIGH-RESOLUTION TEMPERATURE READINGS
section.
LOAD COUNTER [41h]
Loads the 9-bit data from the slope accumulator register into the counter register so that it can be accessed
using the Read Counter [A0h] command. Use of the Load Counter command is explained in detail in the
HIGH-RESOLUTION TEMPERATURE READINGS section.
