Datasheet

DS18S20
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COPY SCRATCHPAD [48h]
This command copies the contents of the scratchpad T
H
and T
L
registers (bytes 2 and 3) to EEPROM. 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 at least 10ms as described in the Powering the
DS18S20 section.
RECALL E
2
[B8h]
This command recalls the alarm trigger values (T
H
and T
L
) from EEPROM and places the data in bytes 2
and 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.
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, parasite powered DS18S20s will pull the bus low,
and externally powered DS18S20s will let the bus remain high. See the Powering the DS18S20 section
for usage information for this command.
Table 2. DS18S20 Function Command Set
COMMAND DESCRIPTION PROTOCOL
1-Wire BUS ACTIVITY
AFTER COMMAND IS
ISSUED
NOTES
TEMPERATURE CONVERSION COMMANDS
Convert T
Initiates temperature
conversion.
44h
DS18S20 transmits conversion
status to master (not applicable
for parasite-powered
DS18S20s).
1
MEMORY COMMANDS
Read
Scratchpad
Reads the entire
scratchpad including the
CRC byte.
BEh
DS18S20 transmits up to 9
data bytes to master. 2
Write
Scratchpad
Writes data into
scratchpad bytes 2 and 3
(T
H
and T
L
).
4Eh
Master transmits 2 data bytes
to DS18S20. 3
Copy
Scratchpad
Copies T
H
and T
L
data
from the scratchpad to
EEPROM.
48h
None
1
Recall E
2
Recalls T
H
and T
L
data
from EEPROM to the
scratchpad.
B8h
DS18S20 transmits recall
status to master.
Read Power
Supply
Signals DS18S20 power
supply mode to the
master.
B4h
DS18S20 transmits supply
status to master.
Note 1:
For parasite-powered DS18S20s, the master must enable a strong pullup on the 1-Wire bus during temperature
conversions and copies from the scratchpad to EEPROM. No other bus activity may take place during this time.
Note 2:
The master can interrupt the transmission of data at any time by issuing a reset.
Note 3:
Both bytes must be written before a reset is issued.