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PDF DS1820 Data sheet ( Hoja de datos )
| Número de pieza | DS1820 | |
| Descripción | 1-Wire Digital Thermometer | |
| Fabricantes | Dallas | |
| Logotipo |  |
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DS1820
DS1820
1–WireTM Digital Thermometer
FEATURES
• Unique 1–WireTM interface requires only one port pin
for communication
• Multidrop capability simplifies distributed temperature
sensing applications
• Requires no external components
• Can be powered from data line
• Zero standby power required
• Measures temperatures from –55°C to +125°C in
0.5°C increments. Fahrenheit equivalent is –67°F to
+257°F in 0.9°F increments
• Temperature is read as a 9–bit digital value.
• Converts temperature to digital word in 200 ms (typ.)
• User–definable, nonvolatile temperature alarm set-
tings
• Alarm search command identifies and addresses
devices whose temperature is outside of pro-
grammed limits (temperature alarm condition)
• Applications include thermostatic controls, industrial
systems, consumer products, thermometers, or any
thermally sensitive system
PIN ASSIGNMENT
DDAALLLALSAS
DDSS18224034
1 23
1 23
BOTTOM VIEW
DS1820
PR35 PACKAGE
See Mech. Drawings
Section
NC
NC
NC
NC
NC
NC
VDD
DQ
1
2
3
4
5
6
7
8
16 NC
15 NC
14 NC
13 NC
12 NC
11 NC
10 NC
9 GND
DS1820S
16–PIN SSOP
See Mech. Drawings
Section
PIN DESCRIPTION
GND
– Ground
DQ – Data In/Out
VDD – Optional VDD
NC – No Connect
DESCRIPTION
The DS1820 Digital Thermometer provides 9–bit tem-
perature readings which indicate the temperature of the
device.
Information is sent to/from the DS1820 over a 1–Wire
interface, so that only one wire (and ground) needs to be
connected from a central microprocessor to a DS1820.
Power for reading, writing, and performing temperature
conversions can be derived from the data line itself with
no need for an external power source.
Because each DS1820 contains a unique silicon serial
number, multiple DS1820s can exist on the same
1–Wire bus. This allows for placing temperature sen-
sors in many different places. Applications where this
feature is useful include HVAC environmental controls,
sensing temperatures inside buildings, equipment or
machinery, and in process monitoring and control.
030598 1/27
1 page  
TEMPERATURE MEASURING CIRCUITRY Figure 4
SLOPE ACCUMULATOR
PRESET
DS1820
COMPARE
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
INC
=0
PRESET
SET/CLEAR
LSB
TEMPERATURE REGISTER
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER
STOP
=0
TEMPERATURE/DATA RELATIONSHIPS Table 1
TEMPERATURE
DIGITAL OUTPUT
(Binary)
+125°C
00000000 11111010
+25°C
00000000 00110010
+1/2°C
00000000 00000001
+0°C
00000000 00000000
–1/2°C
11111111 11111111
–25°C
11111111 11001110
–55°C
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
5 Page 
DS1820
The data obtained from the two reads of the 3–step
routine have the following interpretations:
00 There are still devices attached which have
conflicting bits in this position.
01 All devices still coupled have a 0–bit in this
bit position.
10 All devices still coupled have a 1–bit in this
bit position.
11 There are no devices attached to the 1–Wire
bus.
4. The bus master writes a 0. This deselects ROM2
and ROM3 for the remainder of this search pass,
leaving only ROM1 and ROM4 connected to the
1–Wire bus.
5. The bus master performs two more reads and
receives a 0–bit followed by a 1–bit. This indicates
that all devices still coupled to the bus have 0’s as
their second ROM data bit.
6. The bus master then writes a 0 to keep both ROM1
and ROM4 coupled.
7. The bus master executes two reads and receives
two 0–bits. This indicates that both 1–bits and 0–bits
exist as the third bit of the ROM data of the attached
devices.
8. The bus master writes a 0–bit. This deselects ROM1
leaving ROM4 as the only device still connected.
9. The bus master reads the remainder of the ROM bits
for ROM4 and continues to access the part if
desired. This completes the first pass and uniquely
identifies one part on the 1–Wire bus.
10. The bus master starts a new ROM search sequence
by repeating steps 1 through 7.
11. The bus master writes a 1–bit. This decouples
ROM4, leaving only ROM1 still coupled.
12. The bus master reads the remainder of the ROM bits
for ROM1 and communicates to the underlying logic
if desired. This completes the second ROM search
pass, in which another of the ROMs was found.
13. The bus master starts a new ROM search by repeat-
ing steps 1 through 3.
14. The bus master writes a 1–bit. This deselects
ROM1 and ROM4 for the remainder of this search
pass, leaving only ROM2 and ROM3 coupled to the
system.
15. The bus master executes two read time slots and
receives two zeros.
16. The bus master writes a 0–bit. This decouples
ROM3, and leaving only ROM2.
17. The bus master reads the remainder of the ROM bits
for ROM2 and communicates to the underlying logic
if desired. This completes the third ROM search
pass, in which another of the ROMs was found.
18. The bus master starts a new ROM search by repeat-
ing steps 13 through 15.
19. The bus master writes a 1–bit. This decouples
ROM2, leaving only ROM3.
20. The bus master reads the remainder of the ROM bits
for ROM3 and communicates to the underlying logic
if desired. This completes the fourth ROM search
pass, in which another of the ROMs was found.
Note the following:
The bus master learns the unique ID number (ROM data
pattern) of one 1–Wire device on each ROM Search
operation. The time required to derive the part’s unique
ROM code is:
960 µs + (8 + 3 x 64) 61 µs = 13.16 ms
The bus master is therefore capable of identifying 75 dif-
ferent 1–Wire devices per second.
I/O SIGNALING
The DS1820 requires strict protocols to insure data
integrity. The protocol consists of several types of
signaling on one line: reset pulse, presence pulse, write
0, write 1, read 0, and read 1. All of these signals, with
the exception of the presence pulse, are initiated by the
bus master.
The initialization sequence required to begin any com-
munication with the DS1820 is shown in Figure 11. A
reset pulse followed by a presence pulse indicates the
DS1820 is ready to send or receive data given the cor-
rect ROM command and memory function command.
The bus master transmits (TX) a reset pulse (a low sig-
nal for a minimum of 480 µs). The bus master then
releases the line and goes into a receive mode (RX).
The 1–Wire bus is pulled to a high state via the 5K
pull–up resistor . After detecting the rising edge on the
030598 11/27
11 Page | ||
| Páginas | Total 27 Páginas | |
| PDF Descargar | [ Datasheet DS1820.PDF ] | |
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