DS1825U+T&R【PDF 8/21 页】IC THERMOMETER DIGITAL 8-USOP

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

8 of 21

Byte 8 of the scratchpad is read-only and contains the cyclic redundancy check (CRC) code for bytes 0 through 7

of the scratchpad. The DS1825 generates this CRC using the method described in the CRC GENERATION

section.

Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] command; the data must be

transmitted to the DS1825 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

, T

, and

configuration data from the scratchpad to EEPROM, 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

(including the hard-wired address inputs AD0-AD3)is reloaded into the corresponding scratchpad locations. Data

can also be reloaded from EEPROM to the scratchpad at any time using the Recall E

[B8h] command. The master

can issue read time slots following the Recall E

command and the DS1825 will indicate the status of the recall by

transmitting 0 while the recall is in progress and 1 when the recall is done.

Figure 7. DS1825 MEMORY MAP

SCRATCHPAD (Power-up State)

byte 0 Temperature LSB (50h)

byte 1 Temperature MSB (05h)

EEPROM

byte 2 T

byte 3 T

byte 4 Configuration Register*

Configuration Register*

byte 5 Reserved

byte 6 Reserved

byte 7 Reserved

byte 8 CRC

* Lower four bits of Configuration Register

are hardwired through AD0-AD3

CONFIGURATION REGISTER

Byte 4 of the scratchpad memory is the configuration register, as shown in Figure 8. The configuration register

allows the user to set the conversion resolution using the R0 and R1 bits and read the programmed value of the

address pins. The conversion resolution power-up default is R0 = 1 and R1 = 1 (12-bit resolution). Table 4 shows

the resolution configuration settings and maximum conversion time. Note that there is a direct tradeoff between

resolution and conversion time. AD0-AD3 bits report the pin programmed location information and are sampled at

power-up. In Parasite Power mode, the address pins must be connected to DQ or GND and in V

powered mode,

the address pins must be connected to V

or GND. Pins tied to DQ/V

are reported with a logical 1 and pins tied

to GND are reported as a logical 0. Pins connected to DQ/ V

or GND through a resistor are valid logical 1s or

logical 0s if the resistor is less than 10k. Floating or high impedance (>10kW) connections are indeterminate. Bit 7

and Bit 4 of the configuration register are reserved for internal use and cannot be overwritten.

Figure 8. CONFIGURATION REGISTER FORMAT

Note: Bit 0 through Bit 3 are programmed through the four Location Programming Address pins AD0-AD3.

Reading the configuration register provides location information on up to 16 individual DS1825s.

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

AD3

AD2

AD1

AD0

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