DS2480
Serial 1Wire
TM
Line Driver
DS2480
042498 1/26
FEATURES
Universal, commonground serial port to 1Wire
TM
line driver for MicroLAN
TM
applications
Works with all iButtons and MicroLANcompatible
1Wire slave devices
Communicates at regular and Overdrive 1Wire
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
Selfcalibrating time base with
5% tolerance for
serial and 1Wire communication
Slew rate controlled 1Wire pulldown and active
pullup to accommodate long lines and reduce radi-
ation
Userselectable RXD/TXD polarity minimizes com-
ponent count when interfacing to 5V based RS232
systems or directly to UARTs
Programmable 1Wire timing and driver characteris-
tics accommodate a wide range of MicroLAN configu-
rations at regular speed
Smart protocol combines data and control information
without requiring extra pins
Compatible to optical, IR and RF to RS232 converters
Low cost 8pin SOIC surface mount package
Operates over 4.5V to 5.5V from 40
C to +85
C
PIN ASSIGNMENT
RXD
1W
GND
POL
TXD
V
PP
8
7
6
5
8PIN SOIC
(150 MIL)
NC
V
DD
1
2
3
4
PIN DESCRIPTION
GND
Ground
1W
1Wire Input/Output
NC
No Connection
V
DD
4.5 to 5.5 Volts
V
PP
Optional EPROM
Programming Voltage
POL
RXD/TXD Polarity Select
TXD
Serial Data from UART
RXD
Serial Data to UART
ORDERING INFORMATION
DS2480S
8pin SOIC
DESCRIPTION
The DS2480 is a serial port to 1Wire interface chip that
supports standard and Overdrive speeds. It connects
directly to UARTs and 5V RS232 systems. Interfacing to
RS232C (
12V levels) requires a passive clamping cir-
cuit and one 5V to
12V level translator. Internal timers
relieve the host of the burden of generating the time
critical 1Wire communication waveforms. In contrast
to the DS9097(E) where a full character must be sent by
the host for each 1Wire time slot, the DS2480 can
translate each character into eight 1Wire time slots
thereby increasing the data throughput significantly. In
addition, the DS2480 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 poweron default.
Command codes received from the host's crystal con-
trolled UART serve as a reference to continuously cali-
brate the onchip timing generator. The DS2480 uses a
unique protocol that merges data and control informa-
tion without requiring control pins. This approach main-
tains compatibility to offtheshelf serial to wireless
converters allowing easy realization of 1Wire media
jumpers. The various control functions of the DS2480
are optimized for MicroLAN 1Wire networks and sup-
port the special needs of all current 1Wire devices
including the Crypto iButton, EPROMbased AddOnly
Memories, EEPROM devices and 1Wire Thermome-
ters.
DS2480
042498 2/26
DETAILED PIN DESCRIPTION
PIN
SYMBOL
DESCRIPTION
1
GND
Ground Pin: common ground reference and ground return for 1Wire bus
2
1W
1Wire Input/Output Pin: 1Wire bus with slewratecontrolled pulldown,
active pullup, ability to switch in V
PP
to program EPROM, and ability to switch
in V
DD
through a lowimpedance path to program EEPROM, perform a temper-
ature conversion or operate the Crypto iButton.
3
NC
No Connection Pin.
4
V
DD
Power Input Pin: power supply for the chip and 1Wire pullup voltage. 5V
10%; may be derived from 12V V
PP
with an external voltage regulator.
5
V
PP
EPROM Programming Voltage: 12V supply input for EPROM programming;
if EPROM programming is not required, this pin must be tied to V
DD
. V
PP
must
come up before V
DD
.
6
POL
RXD/TXD Polarity Select: RXD/TXD polarity select; tied to GND for RS232
(12V or 5V) connection, tied to V
DD
for direct connection to UART chip.
7
TXD
Serial Data from UART: data input from host (inverted or true); maximum volt-
age swing 0.3V to V
DD
+ 0.3V; for logic thresholds see DC specifications.
8
RXD
Serial Data to UART: signal output to host; pushpull driver with CMOS com-
patible levels; for true
12V RS232 systems an external leveltranslator must
be provided.
OVERVIEW
The DS2480 directly interfaces a 5V serial communica-
tion 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 date 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 commu-
nication port of the host computer through pin TXD. For
compatibility with activehigh as well as activelow sys-
tems, the incoming signal can be inverted by means of
the polarity input POL. The polarity chosen by hardwir-
ing the logic level of this pin is also valid for the output pin
RXD. If for minimizing the interface hardware an asym-
metry 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.
As data enters the core of the DS2480's logic circuitry, it
is analyzed to separate data and command bytes and to
calibrate the device's timing generator. The timing gen-
erator 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 non
TTL threshold to maximize the noise margin for best
performance on large 1Wire MicroLAN networks.
DS2480
042498 3/26
DS2480 BLOCK DIAGRAM Figure 1
MUX
CONFIGURATION
REGISTER
PROTOCOL
ANALYZER
PROTOCOL
ANALYZER
TIMING
GENERATOR
PROTOCOL
CONVERTER
1WIRE
DRIVER
MS BIT OF SPEED CONTROL
(1 = RXD IS INVERTED)
V
PP
1W
RXD
POL
TXD
DEVICE OPERATION
The DS2480 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 DS2480 requires and gener-
ates a communication protocol of 8 data bits per charac-
ter, 1 stop bit and no parity. It is permissible to use two
stop bits on the TXD line. However, the DS2480 will only
assert a single stop bit on RXD.
When powering up, the DS2480 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 DS2480 and is not translated
into any activity on the 1Wire bus. After this first com-
mand byte the device is ready to receive and execute
any command as described later in this document.
A master reset cycle can also be generated by means of
software. This may be necessary if the host for any rea-
son has lost synchronization with the device. The
DS2480 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 gener-
ate 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 DS2480 requires a
1Wire reset command sent by the host at a data rate of
9600 bps for calibration.
DS2480
042498 4/26
STATE TRANSITION DIAGRAM Figure 2
INACTIVE
COMMAND MODE
CONFIGURATION
CHECK
MODE
TX
ARRIVAL
CODE
SINGLE BIT
FUNCTION
SEARCH
ACCEL.
PULSE
RESET
SOFTWARE
MASTER RESET
TX E3h
TX BYTE
110XSS01
111T11Q1
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
0ZZZVVV1
N.C.
101HSS01
100VSSP1
POWER
ON
ARRIVAL
POWER OFF
CODE = E3h
E3h
100VSSP1
101HSS01
0ZZZVVV1
111T11Q1
110XSS01
E1h
ALL OTHER
CODES
ACC.ON
STR. PULLUP
ARMED
ACC. OFF
STR. PULLUP NOT ARMED
N.C. = UNCONDITIONAL
POWER OFF
GENERATE STRONG
PULLUP TO 5V
LEGEND: V
BINARY VALUE (TYPE OF WRITE TIME SLOT)
SS
1WIRE SPEED SELECTION CODE
P
IF LOGIC 1, GENERATES STRONG PULLUP TO 5V IMMEDIATELY FOLLOWING THE TIME SLOT
T
TYPE OF PULSE; 0 = STRONG PULLUP (5V), 1 = PROGRAMMING PULSE (12V)
Q
1 = ARM STRONG PULLUP AFTER EVERY BYTE; 0 = DISARM
H
SEARCH ACCELERATOR CONTROL; 1 = ACCELERATOR ON, 0 = ACCELERATOR OFF
ZZZ
CONFIGURATION PARAMETER CODE (WRITE), 000 = READ CONFIGURATION PARAMETER
VVV
CONFIGURATION PARAMETER VALUE CODE (WRITE), CONFIGURATION PARAMETER CODE (READ)
X
DON'T CARE
CHECK SEARCH
ACCELERATOR FLAG
DATA MODE
PERFORM SEARCH
SEQUENCE
DS2480
042498 5/26
After the DS2480 has reached the command mode, the
host can send commands such as 1Wire Reset, Pulse,
Configuration, Search Accelerator and Single Bit func-
tions or switch over to the second static state called
Data Mode. In data mode the DS2480 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 tran-
sistor in the 1Wire driver circuit.
While being in the Data Mode the DS2480 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 care-
fully when developing software drivers for the DS2480.
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 DS2480 has to be switched
to Command mode. The host then sends the appropri-
ate 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 DS2480 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 two bits marks the bus arrival.
If the DS2480 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 DS2480 is controlled by a variety of commands. All
command codes are 8 bits long. The most significant bit
of each command code distinguishes between commu-
nication 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 configura-
tion 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 generat-
ing 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 Configura-
tion Commands.
In addition to the command codes explained in the sub-
sequent sections the DS2480 understands the follow-
ing reserved command codes:
E1h
switch to Data Mode
E3h
switch to Command Mode
F1h
pulse termination
Except for these reserved commands, the Search
Accelerator control and the first byte after poweron
reset or master reset cycle, every legal command byte
generates a response byte. The pulse termination code
triggers the response byte of the terminated pulse com-
mand. Illegal command bytes do not generate a com-
mand response byte.
Once the device is switched back from Data Mode to
Command Mode one must not repeat the E3h com-
mand while the Command Mode is still active.
COMMUNICATION COMMANDS
The DS2480 supports four communication function
commands: Reset, Single Bit, Pulse, and Search Accel-
erator control. Details on the assignment of each bit of
the command codes are shown in Table 1. The corre-
sponding command response bytes are detailed in
Table 2. The Reset, Search Accelerator Control and
Single Bit commands include bits to select the 1Wire
communication speed (regular, flexible regular, Over-
drive). Even if a command does not generate activity on
the 1Wire bus, these bits are latched inside the device
and will take effect immediately.
PDF 
ZIP