DS1821 Ver la hoja de datos (PDF) - Maxim Integrated
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DS1821 Datasheet PDF : 19 Pages
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TEMPERATURE MEASURING CIRCUITRY Figure 2
SLOPE ACCUMULATOR
DS1821
PRESET
COMPARE
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
PRESET
SET/CLEAR
LSB
INC
=0
TEMPERATURE REGISTER
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
STOP
=0
OPERATING MODES
The DS1821 has two operating modes: 1-Wire mode and thermostat mode. The power-up operating
mode is determined by the user-programmable T/R¯ bit in the status/configuration register: if T/R¯ = 0 the
device powers-up in 1-Wire mode, and if T/R¯ = 1 the device powers-up in thermostat mode. The T/R¯ bit
is stored in nonvolatile memory (EEPROM), so it will retain its value when the device is powered down.
1-Wire MODE
The DS1821 arrives from the factory in 1-Wire mode (T/R¯ = 0). In this mode, the DQ pin of the DS1821
is configured as a 1-Wire port for communication with a microprocessor using the protocols described in
the 1-Wire BUS SYSTEM section of this datasheet. These communications can include reading and
writing the high and low thermostat trip-point registers (TH and TL) and the configuration register, and
reading the temperature, counter, and slope accumulator registers. Also in this mode, the microprocessor
can initiate and stop temperature measurements as described in the OPERATION – MEASURING
TEMPERATURE section of this datasheet.
The TH and TL registers and certain bits (THF, TLF, T/R¯, POL and 1SHOT) in the status/configuration
register are stored in nonvolatile EEPROM memory, so they will retain data when the device is powered
down. This allows these registers to be pre-programmed when the DS1821 is to be used as a standalone
thermostat. Writes to these nonvolatile registers can take up to 10ms. To avoid data corruption, no
writes to nonvolatile memory should be initiated while a write to nonvolatile memory is in progress.
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