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PDF DS2480B Data sheet ( Hoja de datos )
| Número de pieza | DS2480B | |
| Descripción | Serial 1-Wire Line Driver | |
| Fabricantes | Dallas Semiconductor | |
| Logotipo |  |
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DS2480B
Serial 1-WireTM Line
Driver with Load Sensor
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 ±5%
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
GND
1
8 RXD
1-W 2
NC 3
7 TXD
6 POL
VDD
4
5 VPP
8-Pin SOIC (150-mil)
PIN DESCRIPTION
GND
- Ground
1-W - 1-Wire Input/Output
NC - 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
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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 4800 bps 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 9600 bps 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 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 12–bit sequence on the 1–Wire bus (see
section Search Accelerator 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 sections
Communication Commands and Configuration Commands.
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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
(nothing)
(as sent)
(nothing)
(nothing)
(nothing)
(response)
(nothing)
(nothing)
(nothing)
(nothing)
CD
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 regular 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
regular 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 pull–up to 5V, the threshold current of the load sensor for
“dynamic” strong pullup duration, 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 wave forms if one
selects “Flexible Speed” (see “Communication Commands” for speed selection).
Flexible speed is implemented to improve the performance of large MicroLAN 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 regular 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.
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet DS2480B.PDF ] | |
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