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PDF DS28EA00 Data sheet ( Hoja de datos )
| Número de pieza | DS28EA00 | |
| Descripción | 1-Wire Digital Thermometer | |
| Fabricantes | Dallas Semiconductor | |
| Logotipo |  |
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www.maxim-ic.com
GENERAL DESCRIPTION
The DS28EA00 is a digital thermometer with 9-bit
(0.5 °C) to 12-bit (1/16 °C) resolution and alarm
function with nonvolatile (NV), user-programmable
upper and lower trigger points. Each DS28EA00 has
its unique 64-bit registration number that is factory-
programmed into the chip. Data is transferred serially
through the 1-Wire® protocol, which requires only one
data line and a ground for communication. The
improved 1-Wire front end with hysteresis and glitch
filter enables the DS28EA00 to perform reliably in
large 1-Wire networks. Unlike other 1-Wire thermo-
meters, the DS28EA00 has two additional pins to
implement a sequence detect function. This feature
allows the user to discover the registration numbers
according to the physical device location in a chain,
e.g., to measure the temperature in a storage tower
at different height. If the sequence detect function is
not needed, these pins can be used as general-
purpose input or output. The DS28EA00 can derive
the power for its operation directly from the data line
(“parasite power”), eliminating the need for an
external power supply.
APPLICATIONS
Data Communication Equipment
Process Temperature Monitoring
HVAC Systems
TYPICAL OPERATING CIRCUIT
VDD
1-Wire
Master
PX.Y
(Micro-
controller)
#1
VDD
IO
DS28EA00
PIOB PIOA
GND
#2
VDD
IO
DS28EA00
PIOB PIOA
GND
#3
VDD
IO
DS28EA00
PIOB PIOA
GND
Schematic shows PIOs wired for sequence detect function.
Commands, Registers, and Modes are capitalized for
clarity.
1-Wire is a registered trademark of Dallas Semiconductor.
DS28EA00
1-Wire Digital Thermometer
with Sequence Detect and PIO
SPECIAL FEATURES
Digital Thermometer Measures Temperatures
from -40°C to +85°C
Thermometer Resolution is User-Selectable
from 9 to 12 Bits
Unique 1-Wire Interface Requires Only One
Port Pin for Communication
Each Device has a Unique 64-Bit Factory-
Lasered Registration Number
ROM Multidrop Capability Simplifies
Distributed Temperature-Sensing
Applications
Improved 1-Wire Interface with Hysteresis
and Glitch Filter
User-Definable Nonvolatile (NV) Alarm
Threshold Settings/User Bytes
Alarm Search Command to Quickly Identify
Devices Whose Temperature is Outside of
Programmed Limits
Standard and Overdrive 1-Wire Speed
Two General-Purpose Programmable IO (PIO)
Pins
Chain Function Sharing the PIO Pins to
Detect Physical Sequence of Devices in
Network
Operating Range: 3.0V to 5.5V, -40°C to +85°C
Can be Powered from Data Line
8-Pin µSOP Package
ORDERING INFORMATION
PART
TEMP RANGE
PACKAGE
DS28EA00U+
-40 to +85°C
8-pin µSOP
DS28EA00U+T -40 to +85°C
Tape & Reel
+ Denotes lead-free package.
PIN CONFIGURATION
IO
NC
NC
GND
+1 8
27
36
45
8 pin µSOP
VDD
PIOB
PIOA
NC
Package Outline Drawing 21-0036
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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061907
1 page  
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major function blocks of the DS28EA00. The
device has three main data components: 1) 64-bit Registration Number, 2) 64-bit scratchpad, and 3) alarm and
configuration registers. The 1-Wire ROM Function control unit processes the ROM function commands that allow
the device to function in a networked environment. The device function control unit implements the device-specific
control functions, such as read/write, temperature conversion, setting the chain state for sequence detection, and
PIO access. The CRC generator assists the master verifying data integrity when reading temperatures and
memory data. In the sequence detect process, PIOB functions as an input, while PIOA provides the connection to
the next device. The power supply sensor allows the master to remotely read whether the DS28EA00 has local
power available.
Figure 2 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of the eight
ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional (“Alarm”) Search ROM,
5) Conditional Read ROM, 6) Skip ROM, 7) Overdrive-Skip ROM or 8) Overdrive-Match ROM. Upon completion of
an Overdrive ROM command byte executed at standard speed, the device enters Overdrive mode, where all
subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is
described in Figure 12. After a ROM function command is successfully executed, the device-specific control
functions become accessible and the master may provide any one of the nine available commands. The protocol
for these control function commands is described in Figure 10. All data is read and written least significant bit
first.
Figure 1. DS28EA00 Block Diagram
Internal VDD
VDD Power Supply
Sensor
IO
1-Wire ROM
Function Control
PIOB
(EN\)
64-Bit
Registration #
Device Function
Control
8-Bit CRC
Generator
Alarm and Config
Registers
64-Bit Scratchpad
(ON\)
RCO
PIOA
(DONE\)
Temperature
Sensor
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5 Page 
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
RECALL EEPROM [B8h]
This command recalls the TH and TL alarm trigger values and configuration data from backup EEPROM into their
respective locations in the scratchpad. After having transmitted the command code, the master may issue read
time slots to monitor the completion of the recall process. Recall is completed when the master reads 1-bits instead
of 0-bits. The recall occurs automatically at power-up, not requiring any activity by the master.
PIO ACCESS READ [F5h]
This command reads the PIO logical status and reports it together with the state of the PIO Output Latch in an
endless loop. A PIO Access Read can be terminated at any time with a 1-Wire Reset. PIO Access Read can be
executed in the Chain ON and Chain DONE state. While the device is in Chain ON or Chain DONE state, the PIO
output latch states will always read out as 1s; the PIO pin state may not be reported correctly.
PIO Status Bit Assignment
b7 b6 b5 b4
Complement of b3 to b0
b3
PIOB Output
Latch State
b2
PIOB Pin
State
b1
PIOA Output
Latch State
b0
PIOA Pin
State
The state of both PIO channels is sampled at the same time. The first sampling occurs during the last (most
significant) bit of the command code F5h. The PIO status is then reported to the bus master. While the master
receives the last (most significant) bit of the PIO status byte, the next sampling occurs and so on until the master
generates a 1-Wire Reset. The sampling occurs with a delay of tREH+x from the rising edge of the MS bit of the
previous byte, as shown in Figure 7. The value of "x" is approximately 0.2µs.
Figure 7. PIO Access Read Timing Diagram
MS 2 bits of
previous byte
VTH
IO
LS 2 bits of PIO
Status byte
tREH+x
Sampling Point
Notes:
1 The "previous byte" could be the command code or the data byte resulting from the previous PIO sample.
2 The sample point timing also applies to the PIO Access Write command, with the "previous byte" being the
write confirmation byte (AAh).
PIO ACCESS WRITE [A5h]
The PIO Access Write command writes to the PIO output latches, which control the pulldown transistors of the PIO
channels. In an endless loop this command first writes new data to the PIO and then reads back the PIO status.
This implicit read-after-write can be used by the master for status verification. A PIO Access Write can be termi-
nated at any time with a 1-Wire Reset. The PIO Access Write command is ignored by the device while in Chain ON
or Chain DONE state.
PIO Output Data Bit Assignment
b7 b6 b5 b4 b3 b2
b1
b0
X
X
X
X
X
X
PIOB
PIOA
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