Datasheet

DS1822-PAR
10 of 19
WRITE SCRATCHPAD [4Eh]
This command allows the master to write three bytes of data to the DS1822-PAR’s scratchpad. The first
data byte is written into the T
H
register (byte 2 of the scratchpad), the second byte is written into the T
L
register (byte 3), and the third byte is written into the configuration register (byte 4). Data must be
transmitted least significant bit first. All three bytes MUST be written before the master issues a reset, or
the data may be corrupted.
READ SCRATCHPAD [BEh]
This command allows the master to read the contents of the scratchpad. The data transfer starts with the
least significant bit of byte 0 and continues through the scratchpad until the 9
th
byte (byte 8–CRC) is read.
If only part of the scratchpad contents is required, the master may issue a reset to terminate reading at any
time.
COPY SCRATCHPAD [48h]
This command copies the contents of the scratchpad T
H
, T
L
and configuration registers (bytes 2, 3, and 4)
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
PARASITE POWER section.
RECALL E
2
[B8h]
This command recalls the alarm trigger values (T
H
and T
L
) and configuration data from EEPROM and
places the data in bytes 2, 3, and 4, respectively, in the scratchpad memory. The master device can issue
“read-time slots” (see the 1-WIRE BUS SYSTEM section) following the Recall E
2
command and the
DS1822-PAR 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.
DS1822-PAR FUNCTION COMMAND SET Table 4
Command Description Protocol
1-Wire Bus Activity
After Command is Issued Notes
TEMPERATURE CONVERSION COMMANDS
Convert T Initiates temperature
conversion.
44h None 1
MEMORY COMMANDS
Read
Scratchpad
Reads the entire scratchpad
including the CRC byte.
BEh DS1822-PAR transmits up
to 9 data bytes to master.
2
Write
Scratchpad
Writes data into scratchpad
bytes 2, 3, and 4 (T
H
, T
L
, and
configuration registers).
4Eh Master transmits three data
bytes to DS1822-PAR.
3
Copy
Scratchpad
Copies T
H
, T
L
, and
configuration register data from
the scratchpad to EEPROM.
48h None 1
Recall E
2
Recalls T
H
, T
L
, and
configuration register data from
EEPROM to the scratchpad.
B8h DS1822-PAR transmits
recall status to master.
NOTES:
1. 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.
2. The master can interrupt the transmission of data at any time by issuing a reset.
3. All three bytes must be written before a reset is issued.