DS1825 Maxim Integrated Products, DS1825 Datasheet - Page 5

• Manufacturer Part Number: DS1825
• Description: Programmable Resolution 1-Wire Digital Thermometer
• Manufacturer: Maxim Integrated Products

OPERATION¾MEASURING TEMPERATURE
The core functionality of the DS1825 is its direct-to-digital temperature sensor. The resolution of the temperature
sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and
0.0625°C, respectively. The default resolution at power-up is 12-bit. The DS1825 powers-up in a low-power idle
state; to initiate a temperature measurement and A-to-D conversion, the master must issue a Convert T [44h]
command. Following the conversion, the resulting thermal data is stored in the 12-bit temperature register in the
scratchpad memory and the DS1825 returns to its idle state. If the DS1825 is powered by an external supply, the
master can issue “read time slots” (see the 1-Wire BUS SYSTEM section) after the Convert T command and the
DS1825 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion
is done. If the DS1825 is powered with parasite power, this notification technique cannot be used since the bus
must be pulled high by a strong pullup during the entire temperature conversion. The bus requirements for parasite
power are explained in detail in the POWERING THE DS1825 section of this data sheet.
The DS1825 output temperature data is calibrated in degrees centigrade; for Fahrenheit applications, a lookup
table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extended two’s
complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the temperature is
positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the DS1825 is configured for 12-
bit resolution, all bits in the temperature register will contain valid data. For 11-bit resolution, bit 0 is undefined. For
10-bit resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1 and 0 are undefined. Table 3 gives
examples of digital output data and the corresponding temperature reading for 12-bit resolution conversions.
Figure 2. TEMPERATURE REGISTER FORMAT
Table 3. TEMPERATURE/DATA RELATIONSHIP
OPERATION¾ALARM SIGNALING
After the DS1825 performs a temperature conversion, the temperature value is compared to the user-defined two’s
complement alarm trigger values stored in the 1-byte T
the value is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The T
registers are NV (EEPROM) so they will retain data when the device is powered down. T
through bytes 2 and 3 of the scratchpad as explained in the MEMORY section of this data sheet.
MS Byte
LS Byte
bit 15
bit 7
*The power-on reset value of the temperature register is +85°C
2
S
3
TEMPERATURE
+25.0625°C
-25.0625°C
+10.125°C
-10.125°C
+125°C
+85°C*
+0.5°C
-0.5°C
-55°C
0°C
bit 14
bit 6
2
S
2
bit 13
bit 5
2
S
0000 0111 1101 0000
0000 0101 0101 0000
0000 0001 1001 0001
0000 0000 1010 0010
0000 0000 0000 1000
0000 0000 0000 0000
1111 1111 1111 1000
1111 1111 0101 1110
1111 1110 0110 1111
1111 1100 1001 0000
1
DIGITAL OUTPUT
(Binary)
5 of 21
H
bit 12
bit 4
and T
2
S
0
L
registers (see Figure 3). The sign bit (S) indicates if
bit 11
bit 3
2
S
-1
DIGITAL OUTPUT
FF5Eh
FE6Fh
FC90h
07D0h
00A2h
FFF8h
0550h
0191h
0008h
0000h
(Hex)
bit 10
bit 2
2
2
-2
6
H
and T
bit 1
bit 9
2
L
2
-3
5
can be accessed
H
and T
bit 0
bit 8
2
2
-4
4
L