DS1822-PAR_07 DALLAS [Dallas Semiconductor], DS1822-PAR_07 Datasheet - Page 6

• Manufacturer Part Number: DS1822-PAR_07
• Description: Econo 1-Wire Parasite-Power Digital Thermometer
• Manufacturer: DALLAS [Dallas Semiconductor]

Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] command, and the
data must be transmitted to the DS1822-PAR starting with the least significant bit of byte 2. To verify
data integrity, the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is
written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least
significant bit of byte 0. To transfer the T
the master must issue the Copy Scratchpad [48h] command.
Data in the EEPROM registers is retained when the device is powered down; at power-up the EEPROM
data is reloaded into the corresponding scratchpad locations. Data can also be reloaded from EEPROM to
the scratchpad at any time using the Recall E
(see the 1-WIRE BUS SYSTEM section) following the Recall E
indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is
done.
CONFIGURATION REGISTER
Byte 4 of the scratchpad memory contains the configuration register, which is organized as
illustrated in Figure 7. The user can set the conversion resolution of the DS1822-PAR using the R0 and
R1 bits in this register as shown in Table 3. The power-up default of these bits is R0 = 1 and R1 = 1 (12-
bit resolution). Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits
0-4 in the configuration register are reserved for internal use by the device and cannot be overwritten.
CONFIGURATION REGISTER Figure 7
THERMOMETER RESOLUTION CONFIGURATION Table 3
CRC GENERATION
CRC bytes are provided as part of the DS1822-PAR’s 64-bit ROM code and in the 9
scratchpad memory. The ROM code CRC is calculated from the first 56 bits of the ROM code and is
contained in the most significant byte of the ROM. The scratchpad CRC is calculated from the data stored
in the scratchpad, and therefore it changes when the data in the scratchpad changes. The CRCs provide
the bus master with a method of data validation when data is read from the DS1822-PAR. To verify that
data has been read correctly, the bus master must recalculate the CRC from the received data and then
compare this value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for
scratchpad reads). If the calculated CRC matches the read CRC, the data has been received error free. The
comparison of CRC values and the decision to continue with an operation are determined entirely by the
bus master. There is no circuitry inside the DS1822-PAR that prevents a command sequence from
R1
0
0
1
1
bit 7
0
R0
0
1
0
1
bit 6
R1
bit 5
Resolution
R0
10-bit
11-bit
12-bit
9-bit
H
, T
L
2
bit 4
and configuration data from the scratchpad to EEPROM,
1
[B8h] command. The master can issue “read-time slots”
6 of 19
bit 3
Max Conversion Time
1
93.75 ms
187.5 ms
375 ms
750 ms
bit 2
1
2
command and the DS1822-PAR will
bit 1
1
(t
(t
(t
(t
CONV
CONV
CONV
CONV
bit 0
/8)
/4)
/2)
1
)
th
DS1822-PAR
byte of the