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FEATURES

Universal, common-ground serial port to 1-
Wire

line driver for MicroLAN applications

Works with all iButtons and MicroLAN-
compatible 1-Wire slave devices

Communicates at regular and Overdrive 1-
Wire speed and serial port data rates of 9600
(default), 19200, 57600 and 115200 bps

Supports 12V EPROM programming and stiff
5V pullup for crypto iButton, sensors and
EEPROM

Load sensor to terminate the stiff pullup as
the energy demand of the crypto iButton
drops

Self-calibrating time base with

tolerance for serial and 1-Wire
communication

Slew rate controlled 1-Wire pulldown and
active pullup to accommodate long lines and
reduce radiation

User-selectable RXD/TXD polarity
minimizes component count when interfacing
to 5V based RS232 systems or directly to
UARTs

Programmable 1-Wire timing and driver
characteristics accommodate a wide range of
MicroLAN configurations at regular speed

Smart protocol combines data and control
information without requiring extra pins

Compatible with optical, IR and RF to RS232
converters

Low cost 8-pin SOIC surface mount package

Operates over 4.5V to 5.5V from -40°C to
+85°C

PIN ASSIGNMENT

PIN DESCRIPTION

GND

- Ground

1-W

- 1-Wire Input/Output

- No Connection

VDD

- 4.5 to 5.5 Volts

VPP

- Optional EPROM

Programming Voltage

POL

- RXD/TXD Polarity Select

TXD

- Serial Data from UART

RXD

- Serial Data to UART

ORDERING INFORMATION

DS2480BS

8-pin SOIC

Note: The DS2480B will replace the DS2480
later in 1999. It is fully backward compatible to
software drivers that accept a 0 as well as a 1 for
bit 2 of the Reset-command response byte (see
page 7, Table 2)

DESCRIPTION

The DS2480B is a serial port to 1-Wire interface chip that supports regular and Overdrive speeds. It con-
nects directly to UARTs and 5V RS232 systems. Interfacing to RS232C (± 12V levels) requires a passive
clamping circuit and one 5V to ±12V level translator. Internal timers relieve the host of the burden of
generating the time-critical 1-Wire communication waveforms. In contrast to the DS9097(E) where a full
character must be sent by the host for each 1-Wire time slot, the DS2480B can translate each character

DS2480B

Serial 1-Wire

Line

Driver with Load Sensor

www.dalsemi.com

GND

1-W

VDD

RXD

TXD

POL

VPP

8-Pin SOIC (150-mil)

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into eight 1-Wire time slots, thereby increasing the data throughput significantly. In addition, the
DS2480B can be set to communicate at four different data rates, including 115.2 kbps, 57.6 kbps and 19.2
kbps with 9.6 kbps being the power-on default. Command codes received from the host's crystal
controlled UART serve as a reference to continuously calibrate the on-chip timing generator. The
DS2480B uses a unique protocol that merges data and control information without requiring control pins.
This approach maintains compatibility to off-the-shelf serial to wireless converters, allowing easy
realization of 1-Wire media jumpers. The various control functions of the DS2480B are optimized for
MicroLAN 1-Wire networks and support the special needs of all current 1-Wire devices including the
crypto iButton, EPROM-based Add-Only Memories, EEPROM devices and 1-Wire Thermometers.

DETAILED PIN DESCRIPTION

PIN

SYMBOL

DESCRIPTION

GND

Ground Pin: common ground reference and ground return for 1-Wire bus

1-W

1Wire Input/Output Pin:

1Wire bus with slewratecontrolled pulldown,

active pullup, ability to switch in V

to program EPROM, and ability to switch

in V

through a lowimpedance path to program EEPROM, perform a

temperature conversion or operate the crypto iButton.

No Connection Pin.

Power Input Pin: power supply for the chip and 1Wire pullup voltage, 5V
±10%, must always be lower than V

. V

should be derived from V

by a

separate voltage regulator. If EPROM programming is not required feed V

from V

through a Schottky diode to get a 0.3V drop at V

EPROM Programming Voltage: 12V supply input for EPROM programming.
If EPROM programming is not required, connect this pin directly to the system's
5V supply.

POL

RXD/TXD Polarity Select:

RXD/TXD polarity select; tied to GND for RS232

(12V or 5V) connection; tied to V

for direct connection to UART chip.

TXD

Serial Data from UART:

data input from host (inverted or true); maximum

voltage swing 0.3V to V

+ 0.3V; for logic thresholds see DC specifications.

RXD

Serial Data to UART:

signal output to host; pushpull driver with CMOS

compatible levels; for true

12V RS232 systems an external level translator must

be provided.

OVERVIEW

The DS2480B directly interfaces a 5V serial communication port with its lines TXD (transmit) and RXD
(receive) to a 1Wire bus. In addition the device performs a speed conversion allowing the data rate at the
communication port to be different from the 1Wire data rate. Several parameters relating to the 1Wire
port and its timing as well as the communication speed at both the port and the 1Wire bus are
configurable. The circuit to achieve these functions is outlined in Figure 1, Block Diagram.

The device gets its input data from the serial communication port of the host computer through pin TXD.
For compatibility with activehigh as well as activelow systems, the incoming signal can be inverted by
means of the polarity input POL. The polarity chosen by hardwiring the logic level of this pin is also
valid for the output pin RXD. If for minimizing the interface hardware an asymmetry between RXD and
TXD is desired, this can be achieved by setting the most significant bit of the Speed Control parameter to
a 1 (see Configuration Parameter Value Codes). With the MS bit of the speed control set to 1, the polarity
at TXD is still selected by the logic level at POL, but the polarity at RXD will be the opposite of what the
logic level at POL specifies.

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As data enters the core of the DS2480B's logic circuitry, it is analyzed to separate data and command
bytes and to calibrate the device's timing generator. The timing generator controls all speed relations of
the communication interface and the 1Wire bus as well as the wave forms on the 1Wire bus.

Command bytes either affect the configuration setting or generate certain wave forms on the 1Wire bus.
Data bytes are simply translated by the protocol converter into the appropriate 1Wire activities. Each
data byte generates a return byte from the 1Wire bus that is communicated back to the host through the
RXD pin as soon as the activity on the 1Wire bus is completed.

The 1Wire driver shapes the slopes of the 1Wire wave forms, applies programming pulses or strong
pullup to 5 volts and reads the 1Wire bus using a nonTTL threshold to maximize the noise margin for
best performance on large 1Wire MicroLAN networks.

DS2480B BLOCK DIAGRAM Figure 1

DEVICE OPERATION

The DS2480B can be described as a complex state machine with two static and several dynamic states.
Two deviceinternal flags as well as functions assigned to certain bit positions in the command codes
determine the behavior of the chip, as shown in the state transition diagram (Figure 2). The DS2480B
requires and generates a communication protocol of 8 data bits per character, 1 stop bit and no parity. It is
permissible to use 2 stop bits on the TXD line. However, the DS2480B will only assert a single stop bit
on RXD.

When powering up, the DS2480B performs a master reset cycle and enters the Command Mode, which
is one of the two static states. The device now expects to receive one 1Wire reset command on the TXD
line sent by the host at a data rate of 9600 bits per second (see section Communication Commands for
details). This command byte is required solely for calibration of the timing generator the DS2480B and is
not translated into any activity on the 1Wire bus. After this first command byte the device is ready to
receive and execute any command as described later in this document.

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A master reset cycle can also be generated by means of software. This may be necessary if the host for
any reason has lost synchronization with the device. The DS2480B will perform a master reset cycle
equivalent to the poweron reset if it detects start polarity in place of the stop bit. The host has several
options to generate this condition. These include making the UART generate a break signal, sending a
NULL character at a data rate of 4800 bps and sending any character with parity enabled and selecting
space polarity for the parity bit. As with the poweron reset, the DS2480B requires a 1Wire reset
command sent by the host at a data rate of 9600 bps for calibration.

After the DS2480B has reached the Command Mode, the host can send commands such as 1Wire Reset,
Pulse, Configuration, Search Accelerator and Single Bit functions or switch over to the second static state
called

Data Mode

. In Data Mode the DS2480B simply converts bytes it receives at the TXD pin into

their equivalent 1Wire wave forms and reports the results back to the host through the RXD pin. If the
Search Accelerator is on, each byte seen at TXD will generate a 12bit sequence on the 1Wire bus (see
section Search Accelerator for details). If the strong pullup to 5V is enabled (see Pulse command), each
byte on the 1Wire bus will be followed by a pause of predefined duration where the bus is pulled to 5V
via a low impedance transistor in the 1Wire driver circuit.

While being in the Data Mode the DS2480B checks each byte received from the host for the reserved
code that is used to switch back to Command Mode. To be able to write any possible code (including the
reserved one) to the 1Wire bus, the transition to the Command Mode is as follows: After having
received the code for switching to Command Mode, the device temporarily enters the

Check Mode

where it waits for the next byte. If both bytes are the same, the byte is sent

once

to the 1Wire bus and

the device returns to the Data Mode. If the second byte is different from the reserved code, it will be
executed as command and the device finally enters the Command Mode. As a consequence, if the
reserved code that normally switches to Command Mode is to be written to the 1Wire bus, this code
byte must be sent twice (duplicated). This detail must be considered carefully when developing software
drivers for the DS2480B.

After having completed a memory function with a device on the 1Wire bus it is recommended to issue a
Reset Pulse. This means that the DS2480B has to be switched to Command Mode. The host then sends
the appropriate command code and continues performing other tasks. If during this time a device arrives
at the 1Wire bus it will generate a presence pulse. The DS2480B will recognize this unsolicited presence
pulse and notify the host by sending a byte such as XXXXXX01b. The Xs represent undefined bit values.
The fact that the host receives the byte unsolicited together with the pattern 01b in the least significant 2
bits marks the bus arrival. If the DS2480B is left in Data Mode after completing a memory function
command it will not report any bus arrival to the host.

COMMAND CODE OVERVIEW

The DS2480B is controlled by a variety of commands. All command codes are 8 bits long. The most
significant bit of each command code distinguishes between communication and configuration
commands. Configuration commands access the configuration registers. They can write or read any of the
configurable parameters. Communication commands use data of the configuration register in order to
generate activity on the 1Wire bus and/or (dis)arm the strong pullup after every byte or (de)activate the
Search Accelerator without generating activity on the 1Wire bus. Details on the command codes are
included in the State Transition diagram (Figure 2). A full explanation is given in the subsequent sections
Communication Commands and Configuration Commands.

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