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PDF DS2480B Data sheet ( Hoja de datos )
| Número de pieza | DS2480B | |
| Descripción | Serial 1-Wire Line Driver with Load Sensor | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-5047; 4/15
DS2480B
Serial to 1-Wire Line Driver
BENEFITS AND FEATURES
• Simplifies the Design of a Low-Cost, Universal
RS-232 COM Port to 1-Wire® Interface
True-Ground
o Interface to an RS-232 COM Port for Reading
and Writing 1-Wire Devices
o Works with Bipolar as well as Unipolar Logic
Signals
o Slew Rate Controlled 1-Wire Pulldown and
Active Pullup to Accommodate Long Lines
and Reduce Radiation
o Communicates at Data Rates of 9.6kbps
(default), 19.2kbps, 57.6kbps, and 115.2kbps
o Self-Calibrating Time Base with ±5%
Tolerance for Serial and 1-Wire
Communication
o User-Selectable RXD/TXD Polarity
Minimizes Component Count When
Interfacing to 5V Based RS232 Systems or
Directly to UARTs
o Smart Protocol Combines Data and Control
Information Without Requiring Extra Pins
o Compatible with Optical, IR, and RF to
RS232 Converters
• Single Product Supports Various iButton® or
1-Wire Device Types for Easy System Integration
o Supports Reading and Writing at Standard
and Overdrive Speeds
o Provides Strong Pullup to 5V for Temperature
and EEPROM 1-Wire Devices
o Programs 1-Wire EPROM Devices with
External 12V Power Supply
o Programmable 1-Wire Timing and Driver
Characteristics Accommodate a Wide Range
of Slave Device Configurations at Standard
Speed
o Operates Over 4.5V to 5.5V from -40°C to
+85°C
PIN ASSIGNMENT
GND
1
8 RXD
1-W 2
NC 3
7 TXD
6 POL
VDD
4
5 VPP
8-Pin SO (150 mil)
PIN DESCRIPTION
GND
- Ground
1-W - 1-Wire Input/Output
NC - No Connection
VDD - 4.5V to 5.5V
VPP - Optional EPROM
Programming Voltage
POL
- RXD/TXD Polarity Select
TXD
- Serial Data from UART
RXD
- Serial Data to UART
ORDERING INFORMATION
PART
DS2480B+
TEMP
PIN-
RANGE PACKAGE
-40°C to +85°C 8 SO
DS2480B+T&R -40°C to +85°C 8 SO
+ Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
1-Wire and iButton are registered trademarks of
Maxim Integrated Products, Inc.
DESCRIPTION
The DS2480B is a serial port to 1-Wire interface chip that supports standard 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
Maxim Integrated 1
1 page  
DS2480B
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 power-on 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 4800bps and sending any character with parity enabled and selecting
space polarity for the parity bit. As with the power-on reset, the DS2480B requires a 1-Wire reset
command sent by the host at a data rate of 9600bps for calibration.
After the DS2480B has reached the Command Mode, the host can send commands such as 1-Wire 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 1-Wire waveforms 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 12-bit sequence on the 1-Wire bus
(see Search Accelerator section for details). If the strong pullup to 5V is enabled (see Pulse Command),
each byte on the 1-Wire bus will be followed by a pause of predefined duration where the bus is pulled to
5V via a low-impedance transistor in the 1-Wire 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 1-Wire 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 1-Wire 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 1-Wire 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 1-Wire 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 1-Wire 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 1-Wire bus and/or (dis)arm the strong pullup after every byte or (de)activate the
Search Accelerator without generating activity on the 1-Wire bus. Details on the command codes are
included in the State Transition diagram (Figure 2). A full explanation is given in the subsequent
Communication Commands and Configuration Commands sections.
Maxim Integrated ............................................................................................................................................................................................. 5
5 Page 
Search Accelerator Usage Example
Action Sequence
Generate Reset Pulse
Set Data Mode
Search ROM command
Set Command Mode
Search Accelerator On
Set Data Mode
Send 16 bytes
Set Command Mode
Search Accelerator Off
Set Data Mode
Do Memory Function
Set Command Mode
Generate Reset Pulse
Host TX
C1
E1
F0
E3
B1
E1
data
E3
A1
E1
E3
C1
DS2480B
Host RX
CD or ED
(nothing)
(as sent)
(nothing)
(nothing)
(nothing)
(response)
(nothing)
(nothing)
(nothing)
(nothing)
CD or ED
CONFIGURATION COMMANDS
The DS2480B is designed to be configurable for the varying requirements of its application. When the
device powers up and/or performs a master reset cycle, the hard-wired default configuration settings take
effect. These settings will work on a short 1-Wire bus and assume standard 1-Wire communication speed.
To change these default settings and to verify the current settings, the logic of the DS2480B supports
configuration commands. A summary of the available configuration parameters, their default settings at
standard and Overdrive speed and their applicability is shown in Table 3.
Parameters not related to the communication speed on the 1-Wire bus specify the duration of the 12V
programming pulse, the duration of the strong pullup to 5V, and the baud rate on the interface that
connects the DS2480B to the host. The remaining three parameters are used to modify the 1-Wire
communication waveforms if one selects “Flexible Speed” (see Communication Commands for speed
selection).
Flexible speed is implemented to improve the performance of large 1-Wire Networks. This is
accomplished by:
limiting the slew rate on falling edges (e. g., at the beginning of time slots, to reduce ringing),
extending the Write-1 low time (allows the current flow through the network to end slowly, to prevent
voltage spikes from inductive kickback),
delaying the time point when reading a bit from the 1-Wire bus (gives the network more time to
stabilize, to get a higher voltage margin) and
adding extra recovery time between Write-0 time slots (allows more energy transfer through the
network, to replenish the parasite power supply of the devices on the bus).
The latter two functions are controlled by a single parameter. Taking advantage of flexible speed requires
changing one or more of these parameters from their default values. Otherwise the waveforms will be
identical to those at standard speed.
Each configuration parameter is identified by its 3-bit parameter code and can be programmed for one of
a maximum eight different values using a 3-bit value code. A matrix of parameter codes and value codes
with the associated physical values in shown in Table 4.
Maxim Integrated ........................................................................................................................................................................................... 11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet DS2480B.PDF ] | |
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