Rainbow Electronics DS18B20-PAR - Manual (Page 6)

DS18B20-PAR
6 of 19
DS18B20-PAR MEMORY MAP cáÖìêÉ=S
SCRATCHPAD (Power-up State)
byte 0 Temperature LSB (50h)
byte 1 Temperature MSB (05h) EEPROM
byte 2 T
H
Register or User Byte 1* T
H
Register or User Byte 1
byte 3 T
L
Register or User Byte 2* T
L
Register or User Byte 2
byte 4 Configuration Register* Configuration Register
byte 5 Reserved (FFh)
byte 6 Reserved (0Ch)
byte 7 Reserved (10h)
byte 8 CRC*
* Power-up state depends on value(s) stored
in EEPROM
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 DS18B20-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; these
bits will return 1s when read.
CONFIGURATION REGISTER Figure 7
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
0 R1 R0 1 1 1 1 1
THERMOMETER RESOLUTION CONFIGURATION Table 3
R1 R0 Resolution Max Conversion Time
0 0 9-bit 93.75 ms (t
CONV
/8)
0 1 10-bit 187.5 ms (t
CONV
/4)
1 0 11-bit 375 ms (t
CONV
/2)
1 1 12-bit 750 ms (t
CONV
)
CRC GENERATION
CRC bytes are provided as part of the DS18B20-PAR’s 64-bit ROM code and in the 9
th
byte of the
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 DS18B20-PAR. To
(85°C)