Datasheet
DS18S20 Operation Example 3
In this example there is only one DS18S20 on the bus and it is using parasite power. The bus master initiates a tempera-
ture conversion then reads the DS18S20 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.
Tx Presence DS18S20 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 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 rst 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 responds with presence pulse.
— —
CPU calculates extended resolution temperature using the equation in
the Operation—Measuring Temperature section.
DS18S20 High-Precision 1-Wire Digital Thermometer
www.maximintegrated.com
Maxim Integrated
│
19