DS18S20
High-Precision 1-Wire Digital Thermometer
Convert T [44h]
Copy Scratchpad [48h]
This command initiates a single temperature conversion.
Following the conversion, the resulting thermal data is
stored in the 2-byte temperature register in the scratch-
pad memory and the DS18S20 returns to its low-power
idle state. If the device is being used in parasite power
mode, within 10µs (max) after this command is issued the
master must enable a strong pullup on the 1-Wire bus for
This command copies the contents of the scratchpad T
and T registers (bytes 2 and 3) to EEPROM. If the device
L
is being used in parasite power mode, within 10µs (max)
after this command is issued the master must enable
a strong pullup on the 1-Wire bus for at least 10ms as
described in the Powering The DS18S20 section.
H
2
Recall E [B8h]
the duration of the conversion (t
) as described in the
CONV
This command recalls the alarm trigger values (T and
H
Powering The DS18S20 section. If the DS18S20 is pow-
ered by an external supply, the master can issue read-
time slots after the Convert T command and the DS18S20
will respond by transmitting 0 while the temperature con-
version is in progress and 1 when the conversion is done.
In parasite power mode this notification technique cannot
be used since the bus is pulled high by the strong pullup
during the conversion.
T ) from EEPROM and places the data in bytes 2 and
L
3, respectively, in the scratchpad memory. The master
device can issue read-time slots following the Recall E
2
command and the DS18S20 will indicate the status of the
recall by transmitting 0 while the recall is in progress and
1 when the recall is done. The recall operation happens
automatically at power-up, so valid data is available in
the scratchpad as soon as power is applied to the device.
Write Scratchpad [4Eh]
This command allows the master to write 2 bytes of data
to the DS18S20’s scratchpad. The first byte is written into
Read Power Supply [B4h]
The master device issues this command followed by a
read-time slot to determine if any DS18S20s on the bus
are using parasite power. During the read-time slot, para-
site powered DS18S20s will pull the bus low, and exter-
nally powered DS18S20s will let the bus remain high. See
the Powering The DS18S20 section for usage information
for this command.
the T register (byte 2 of the scratchpad), and the second
H
byte is written into the T register (byte 3 of the scratch-
L
pad). Data must be transmitted least significant bit first.
Both bytes MUST be written before the master issues a
reset, or the data may be corrupted.
Read Scratchpad [BEh]
1-Wire Signaling
This command allows the master to read the contents of
the scratchpad. The data transfer starts with the least sig-
nificant bit of byte 0 and continues through the scratchpad
until the 9th byte (byte 8 – CRC) is read. The master may
issue a reset to terminate reading at any time if only part
of the scratchpad data is needed.
The DS18S20 uses a strict 1-Wire communication pro-
tocol to ensure data integrity. Several signal types are
defined by this protocol: reset pulse, presence pulse,
write 0, write 1, read 0, and read 1. All these signals, with
the exception of the presence pulse, are initiated by the
bus master.
Maxim Integrated
│ 12
www.maximintegrated.com
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
