Datasheet

DS18S20-PAR
17 of 20
DS18S20-PAR OPERATION EXAMPLE 2
In this example there are multiple DS18S20-PARs on the bus. The bus master initiates a temperature
conversion in a specific DS18S20-PAR and then reads its scratchpad and recalculates the CRC to verify
the data.
MASTER MODE DATA (LSB FIRST) COMMENTS
TX Reset Master issues reset pulse.
RX Presence DS18S20-PARs respond with presence pulse.
TX 55h Master issues Match ROM command.
TX 64-bit ROM code Master sends DS18S20-PAR ROM code.
TX 44h Master issues Convert T command.
TX DQ line held high by
strong pullup
Master applies strong pullup to DQ for the duration of the
conversion (t
conv
).
TX Reset Master issues reset pulse.
RX Presence DS18S20-PARs respond with presence pulse.
TX 55h Master issues Match ROM command.
TX 64-bit ROM code Master sends DS18S20-PAR ROM code.
TX BEh Master issues Read Scratchpad command.
RX 9 data bytes Master reads entire scratchpad including CRC. The master
then recalculates the CRC of the first eight data bytes from the
scratchpad and compares the calculated CRC with the read
CRC (byte 9). If they match, the master continues; if not, the
read operation is repeated.
DS18S20-PAR OPERATION EXAMPLE 3
In this example there is only one DS18S20-PAR on the bus. The bus master initiates a temperature
conversion then reads the DS18S20-PAR scratchpad and calculates a higher resolution result using the
data from the temperature, COUNT REMAIN and COUNT PER °C registers.
MASTER MODE DATA (LSB FIRST) COMMENTS
TX Reset Master issues reset pulse.
TR Presence DS18S20-PAR responds with presence pulse.
TX CCh Master issues Skip ROM command.
TX 44h Master issues Convert T command.
TX DQ line held high by
strong pullup
Master applies strong pullup to DQ for the duration of the
conversion (t
conv
).
TX Reset Master issues reset pulse.
RX Presence DS18S20-PAR responds with presence pulse.
TX CCh Master issues Skip ROM command.
TX BEh Master issues Read Scratchpad command.
RX 9 data bytes Master reads entire scratchpad including CRC. The master
then recalculates the CRC of the first eight data bytes from the
scratchpad and compares the calculated CRC with the read
CRC (byte 9). If they match, the master continues; if not, the
read operation is repeated. The master also calculates the
TEMP_READ value and stores the contents of the COUNT
REMAIN and COUNT PER °C registers.
TX Reset Master issues reset pulse.
RX Presence DS18S20-PAR responds with presence pulse.
- - CPU calculates extended resolution temperature using the
equation in the OPERATION - MEASURING
TEMPERATURE section of this datasheet.