19-5860; Rev 12/16
DS2401
Silicon Serial Number
BENEFITS AND FEATURES
•
Guaranteed Unique 64-Bit ROM ID Chip for
Absolute Traceability
o
Unique, Factory-Lasered and Tested
64-Bit Registration Number (8-Bit Family
Code +48-Bit Serial Number + 8-Bit CRC
Tester)
o
8-Bit Family Code Specifies DS2401
Communications Requirements to Reader
Minimalist 1-Wire® Interface Lowers Cost
and Interface Complexity
o
Multiple DS2401 Devices Can Reside on
a Common 1-Wire Net
o
Built-In Multidrop Controller Ensures
Compatibility with Other 1-Wire Net
Products
o
Reduces Control, Address, Data, and
Power to a Single Pin and Communicates
at Up to 16.3kbps
o
Presence Pulse Acknowledges When the
Reader First Applies Voltage
o
Low-Cost TO-92, SOT-223, and TSOC
Surface-Mount Packages
o
TO-92 Tape-and-Reel Version with Leads
Bent to 100-mil Spacing (Default) or with
Straight Leads (DS2401-SL)
Wide Voltage and Temperature Operating
Ranges Enables Robust System Performance
o
Extended 2.8V to 6.0V Range
o
Zero Standby Power Required
o
-40°C to +85°C Industrial Temperature
Range
PIN CONFIGURATIONS
TO-92
TSOC
DS2401
TOP VIEW
•
1
2
3
1 2 3
TOP VIEW
BOTTOM VIEW
Flip Chip, Top View
with Laser Mark,
Contacts Not Visible.
“rrd” = Revision/Date
01rrd
1
2
TOP VIEW
DS2401
+
A
1
2
B
1
2
WLP
APPLICATIONS
PCB Identification
Network Node ID
Equipment Registration
PIN DESCRIPTIONS
PIN
NAME
DATA
(DQ)
GROUND
N.C. (No
Connect)
TO-92
2
1
3
SOT-
223
2
1, 4
3
TSOC
2
1
3–6
FLIP-
CHIP
1
2
—
WLP
A1, B1
A2, B2
—
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
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DS2401
ORDERING INFORMATION
PART
DS2401+
DS2401+T&R
DS2401-SL+T&R
DS2401P+
DS2401P+T&R
DS2401Z+
DS2401Z+T&R
DS2401X1-S#T
DS2401X-S+T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
3 TO-92
3 TO-92 (formed leads)
3 TO-92 (straight leads)
6 TSOC
6 TSOC
4 SOT-223
4 SOT-223
2 Flip Chip (2.5k pieces)
4 WLP
+Denotes
a lead(Pb)-free/RoHS-compliant package.
T&R/T = Tape and reel.
SL = Straight leads.
#Denotes a RoHS-compliant device that may include lead that is exempt under the RoHS requirements.
DESCRIPTION
The DS2401 enhanced silicon serial number is a low-cost, electronic registration number that provides an
absolutely unique identity which can be determined with a minimal electronic interface (typically, a
single port pin of a microcontroller). The DS2401 consists of a factory-lasered, 64-bit ROM that includes
a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (01h). Data is transferred serially
via the 1-Wire protocol that requires only a single data lead and a ground return. Power for reading and
writing the device is derived from the data line itself with no need for an external power source. The
DS2401 is an upgrade to the DS2400. The DS2401 is fully reverse-compatible with the DS2400 but
provides the additional multi-drop capability that enables many devices to reside on a single data line.
The familiar TO-92, SOT-223 or TSOC package provides a compact enclosure that allows standard
assembly equipment to handle the device easily.
OPERATION
The DS2401’s internal ROM is accessed via a single data line. The 48-bit serial number, 8-bit family
code and 8-bit CRC are retrieved using the Maxim 1-Wire protocol. This protocol defines bus
transactions in terms of the bus state during specified time slots that are initiated on the falling edge of
sync pulses from the bus master. All data is read and written least significant bit first.
1-Wire BUS SYSTEM
The 1-Wire bus is a system which has a single bus master system and one or more slaves. In all instances,
the DS2401 is a slave device. The bus master is typically a microcontroller. The discussion of this bus
system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire
signaling (signal type and timing).
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to
drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have an
open-drain connection or 3-state outputs. The DS2401 is an open-drain part with an internal circuit
equivalent to that shown in Figure 2. The bus master can be the same equivalent circuit. If a bidirectional
pin is not available, separate output and input pins can be tied together. The bus master requires a pullup
resistor at the master end of the bus, with the bus master circuit equivalent to the one shown in Figure 3.
The value of the pullup resistor should be approximately 5kΩ for short line lengths. A multidrop bus
consists of a 1-Wire bus with multiple slaves attached. The 1-Wire bus has a maximum data rate of
16.3kbits per second.
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DS2401
The idle state for the 1-Wire bus is high. If, for any reason, a transaction needs to be suspended, the bus
MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low
for more than 120µs, one or more of the devices on the bus may be reset.
DS2401 MEMORY MAP
Figure 1
8-Bit CRC Code
MSB
LSB MSB
48-Bit Serial Number
LSB
8-Bit Family Code (01h)
MSB
LSB
DS2401 EQUIVALENT CIRCUIT
Figure 2
BUS MASTER CIRCUIT
Figure 3
A) Open Drain
V
PUP
See note
To data connection
of DS2401
B) Standard TTL
V
PUP
See note
To data connection
of DS2401
Note:
Depending on the 1-Wire communication speed and the bus load characteristics, the optimal pullup
resistor (R
PU
) value will be in the 1.5kΩ to 5kΩ range.
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DS2401
TRANSACTION SEQUENCE
The sequence for accessing the DS2401 via the 1-Wire port is as follows:
Initialization
ROM Function Command
Read Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by a Presence Pulse(s) transmitted by the
slave(s).
The Presence Pulse lets the bus master know that the DS2401 is on the bus and is ready to operate. For
more details, see the 1-Wire Signaling section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the four ROM function commands. All
ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure
4).
Read ROM [33h] or [0Fh]
This command allows the bus master to read the DS2401’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command can only be used if there is a single DS2401 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open drain will produce a wired-AND result). The DS2401 Read ROM function will occur with a
command byte of either 33h or 0Fh in order to ensure compatibility with the DS2400, which will only
respond to a 0Fh command word with its 64-bit ROM data.
Match ROM [55h] / Skip ROM [CCh]
The complete 1-Wire protocol for all Maxim iButtons® contains a Match ROM and a Skip ROM
command. Since the DS2401 contains only the 64-bit ROM with no additional data fields, the Match
ROM and Skip ROM are not applicable and will cause no further activity on the 1-Wire bus if executed.
The DS2401 does not interfere with other 1-Wire parts on a multidrop bus that do respond to a Match
ROM or Skip ROM (for example, a DS2401 and DS1994 on the same bus).
Search ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the
1-Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process
of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The ROM search process
is the repetition of a simple 3-step routine: read a bit, read the complement of the bit, then write the
desired value of that bit. The bus master performs this simple 3-step routine on each bit of the ROM.
After one complete pass, the bus master knows the contents of the ROM in one device. The remaining
number of devices and their ROM codes may be identified by additional passes. Refer to
Application
Note 187: 1-Wire Search Algorithm
for a comprehensive discussion of a ROM search, including an actual
example.
iButton is a registered trademark of Maxim Integrated Products, Inc.
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DS2401
1-Wire SIGNALING
The DS2401 requires a strict protocol to ensure data integrity. The protocol consists of four types of
signaling on one line: reset sequence with Reset Pulse and Presence Pulse, write 0, write 1, and read data.
All these signals except Presence Pulse are initiated by the bus master.
The initialization sequence required to begin any communication with the DS2401 is shown in Figure 5.
A reset pulse followed by a Presence Pulse indicates the DS2401 is ready to send or receive data given
the correct ROM command.
The bus master transmits (T
X
) a reset pulse (t
RSTL
, minimum 480µs). The bus master then releases the
line and goes into receive mode (R
X
). The 1-Wire bus is pulled to a high state via the 5kΩ pullup resistor.
After detecting the rising edge on the data pin, the DS2401 waits (t
PDH
, 15-60µs) and then transmits the
Presence Pulse (t
PDL
, 60-240µs). The 1-Wire bus requires a pullup resistor range of 1.5kΩ to 5kΩ,
depending on bus load characteristics.
READ/WRITE TIME SLOTS
The definitions of write and read time slots are illustrated in Figure 6. All time slots are initiated by the
master driving the data line low. The falling edge of the data line synchronizes the DS2401 to the master
by triggering a delay circuit in the DS2401. During write time slots, the delay circuit determines when the
DS2401 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay circuit
determines how long the DS2401 will hold the data line low overriding the “1” generated by the master.
If the data bit is a 1, the DS2401 will leave the read data time slot unchanged.
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Embedded System
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