1-Wire Digital Thermometer with
Sequence Detect and PIO
DS28EA00
Maxim Integrated
5
Pin Description
PIN
NAME
FUNCTION
1
IO
1-Wire Bus Interface and Parasitic Power Supply. Open-drain pin that requires external pullup
resistor.
2, 3, 5
N.C.
No Connection
4
GND
Ground Supply
6
PIOA (DONE)
Open-Drain PIOA Channel and Chain Output. For sequence detection, PIOA must be connected to
PIOB of the next device in the chain; leave open or connect to GND for the last device in the
chain.
7
PIOB (EN)
Open-Drain PIOB Channel and Chain Input. For sequence detection, PIOB of the first device in the
chain must be connected to GND.
8
V
DD
Power Supply. Must be connected to GND for operation in parasite-power mode.
Detailed Description
The Block Diagram shows the relationships between
the major function blocks of the DS28EA00. The device
has three main data components: 64-bit registration
number, 64-bit scratchpad, and alarm and configura-
tion 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-spe-
cific control functions, such as read/write, temperature
conversion, setting the chain state for sequence detec-
tion, and PIO access. The cyclic redundancy check
(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 1 shows the hierarchical structure of the 1-Wire
protocol. The bus master must first provide one of the
eight ROM function commands: Read ROM, Match
ROM, Search ROM, Conditional (Alarm) Search ROM,
Conditional Read ROM, Skip ROM, Overdrive-Skip
ROM, Overdrive-Match ROM.
Upon completion of an overdrive ROM command exe-
cuted 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 11. After a
ROM function command is successfully executed, the
device-specific control functions become accessible
and the master can provide any one of the nine avail-
able commands. The protocol for these control function
commands is described in Figure 9. All data is read
and written least significant (LS) bit first.
64-Bit Registration Number
Each DS28EA00 contains a unique registration number
that is 64 bits long. The first 8 bits are a 1-Wire family
code. The next 48 bits are a unique serial number. The
last 8 bits are a CRC of the first 56 bits (see Figure 2 for
details). The 1-Wire CRC is generated using a polyno-
mial generator consisting of a shift register and XOR
gates as shown in Figure 3. The polynomial is X
8
+ X
5
+
X
4
+ 1. Additional information about the 1-Wire CRC is
available in Application Note 27: Understanding and
Using Cyclic Redundancy Checks with Maxim i
Button
?/DIV>
Products.
The shift register bits are initialized to 0. Then starting
with the least significant bit of the family code, one bit
at a time is shifted in. After the eighth bit of the family
code has been entered, then the 48-bit serial number is
entered. After the last byte of the serial number has
been entered, the shift register contains the CRC value.
Shifting in the 8 bits of CRC returns the shift register to
all 0s.
i
Button is a registered trademark of Maxim Integrated Products, Inc.