DS1820
TEMPERATURE MEASURING CIRCUITRY
Figure 4
SLOPE ACCUMULATOR
PRESET
COMPARE
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
PRESET
SET/CLEAR
LSB
INC
=0
TEMPERATURE REGISTER
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
=0
STOP
TEMPERATURE/DATA RELATIONSHIPS
Table 1
TEMPERATURE
+125°C
+25°C
+
1/2
°C
+0°C
–
1
/
2
°C
–25°C
–55°C
DIGITAL OUTPUT
(Binary)
00000000 11111010
00000000 00110010
00000000 00000001
00000000 00000000
11111111 11111111
11111111 11001110
11111111 10010010
DIGITAL OUTPUT
(Hex)
00FA
0032h
0001h
0000h
FFFFh
FFCEh
FF92h
OPERATION – ALARM SIGNALING
After the DS1820 has performed a temperature conver-
sion, the temperature value is compared to the trigger
values stored in TH and TL. Since these registers are
8–bit only, the 0.5°C bit is ignored for comparison. The
most significant bit of TH or TL directly corresponds to
the sign bit of the 16–bit temperature register. If the
result of a temperature measurement is higher than TH
or lower than TL, an alarm flag inside the device is set.
This flag is updated with every temperature measure-
ment. As long as the alarm flag is set, the DS1820 will
respond to the alarm search command. This allows
many DS1820s to be connected in parallel doing simul-
taneous temperature measurements. If somewhere the
temperature exceeds the limits, the alarming device(s)
can be identified and read immediately without having to
read non–alarming devices.
030598 5/27
DALLAS [ DALLAS SEMICONDUCTOR ]
