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DS2490 Schematic ( PDF Datasheet ) - Dallas Semiconducotr

Teilenummer DS2490
Beschreibung USB to 1-Wire Bridge Chip
Hersteller Dallas Semiconducotr
Logo Dallas Semiconducotr Logo 




Gesamt 30 Seiten
DS2490 Datasheet, Funktion
19-4993; 10/09
www.maxim-ic.com
FEATURES
Communicates at regular and overdrive 1-
Wire® speeds
Supports stiff 5V pullup for EEPROM,
sensors, and crypto iButton®
Slew rate controlled 1-Wire timing and active
pullup to accommodate long 1-Wire network
lines and reduce radiation
Programmable 1-Wire timing and driver
characteristics accommodate a wide range of
1-Wire network configurations
Low- to high-level command types, including
macros, for generating 1-Wire communication
Crystal oscillator timebase provides precision
timed 1-Wire waveforms
High-speed 12Mbps Universal Serial Bus
(USB) interface
Integrated USB-compliant transceiver
Supports USB remote wake-up from a 1-Wire
device event to resume a suspended host
system
0oC to +70oC operating temperature range
DS2490
USB to 1-Wire Bridge Chip
PIN ASSIGNMENT
PMOD
NC
NC
NC
VB
SUSO
D-
D+
NC
1-WIRE
NC
GND
1
2
3
4
5
6
7
8
9
10
11
12
24 VD
23 NC
22 NC
21 NC
20 XO
19 XI
18 NC
17 VD2
16 NC
15 NC
14 NC
13 NC
24-Pin SO
Top View
(300-mil)
ORDERING INFORMATION
PART NUMBER
TEMP
RANGE
PIN-PACKAGE
DS2490S+
0oC to +70oC 24 SO (300 mil)
DS2490S+T&R
0oC to +70oC 24 SO (300mil)
+ Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
DESCRIPTION
The DS2490 is a bridge chip that enables communication between a USB host system and a 1-Wire bus.
It provides regular, overdrive, and flexible 1-Wire communication speeds and a full-speed 12Mbps
connection to USB. USB vendor-specific commands defined in this specification are used to control the
DS2490 and communicate with attached 1-Wire devices. A functional block diagram of the DS2490 is
shown in Figure 1.
1-Wire and iButton are registered trademarks of Maxim Integrated Products, Inc.
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DS2490 Datasheet, Funktion
DS2490
or lower should be used. If the fall time is shorter, a parameter code of 0x5 or higher should be used.
Once determined, the value code for the PULLDOWN SLEW RATE control parameter should be stored
in the host and always be loaded into the DS2490 after a power-on or master reset cycle.
1-WIRE TIMING DIAGRAMS
This section explains the 1-Wire bus waveforms generated by the DS2490. First, the communication
waveforms such as the reset/presence detect sequence and read/write data time slots are discussed
followed by a detailed description of the Pulse function under various conditions.
1-Wire Communication Wave Forms
One of the major features of the DS2490 is that it relieves the host from generating the timing of the 1-
Wire signals and sampling the 1-Wire bus at the appropriate times. The reset/presence detect sequence is
shown in Figure 5. This sequence is composed of four timing segments: the reset low time tRSTL, the
short/interrupt sampling offset tSI, the presence detect sampling offset tPDT and a delay time tFILL. The
timing segments tSI, tPDT and tFILL comprise the reset high time tRSTH where 1-Wire slave devices assert
their presence or interrupt pulse. During this time, the DS2490 pulls the 1-Wire bus high with a weak
pullup current.
Reset/presence timing values are shown in Figure 5. The values of all timing segments for all 1-Wire
speed options are shown in the table. Since the reset/presence sequence is slow compared to the time
slots, the values for regular and flexible speed are the same. Except for the falling edge of the presence
pulse, all edges are controlled by the DS2490. The shape of the uncontrolled falling edge is determined
by the capacitance of the 1-Wire bus and the number, speed, and sink capability of the slave devices
connected.
RESET/PRESENCE DETECT Figure 5
SPEED
REGULAR
OVERDRIVE
FLEXIBLE
NOMINAL TIMING VALUES
tRSTL
512µs
tSI
8µs
tPDT
64µs
tFILL
512µs
64µs 2µs 8µs 64µs
512µs
8µs
64µs
512µs
tRSTH
584µs
74µs
584µs
Upon executing a 1-WIRE RESET command (see COMMUNICATION COMMANDS), the DS2490
pulls the 1-Wire bus low for tRSTL and then lets it go back to 5V. The DS2490 will now wait for the
short/interrupt sampling offset tSI to expire and then test the voltage on the 1-Wire bus to determine if
there is a short or an interrupt signal. If there is no short or interrupt the DS2490 will wait for tPDT and test
the voltage on the 1-Wire bus for a presence pulse. Regardless of the result of the presence test, the
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DS2490 pdf, datenblatt
DS2490
Notes:
1. The only valid configuration values are 0 and 1 for the SET_CONFIGURATION request.
Configuration value 0 corresponds to the non-configured state.
2. Only the DEVICE and CONFIGURATION descriptor types are supported for the
GET_DESCRIPTOR request.
3. Interface 0 is the only valid interface value for the DS2490.
4. The only valid feature selector for the command is DEVICE_REMOTE_WAKE-UP.
5. The DS2490 is intended, at a minimum, to be partially bus powered. Remote wake-up can be enabled
or disabled. GET_STATUS requests to the device will return a logic 0 for the self-powered bit field
and the current state value for the remote wake-up bit.
6. There is no USB core level status information defined for interfaces in USB Specification v1.1. The
DS2490 will always return 0 value data for GET_STATUS requests to interfaces.
DS2490 Vendor-Specific USB Commands
Three different vendor-specific command types exist to control and communicate with the DS2490:
Control, Communication, and Mode. Control commands are used to manage various device functions
including the processing of communication commands, buffer clearing, and SW reset. Communication
commands are used for 1-Wire data and command I/O. Mode commands are used to establish the 1-Wire
operational characteristics of the DS2490 such as slew rate, low time, strong pullup, etc. Control,
Communication and Mode commands, like USB core requests, are communicated over the default control
pipe at EP0. With one exception as noted below, each command and any associated parameter data are
individually formatted into the 8-byte control transfer setup packet as follows:
bmRequestType
bRequest
wValue
wIndex
wLength
Request type bit map Command Type
Command Command Parameters (2 bytes)
(1 byte)
(1 byte)
(2 bytes)
(2 bytes)
See Note 2
See Note 1
Notes:
1. The one exception to wValue formatting is for the READ STRAIGHT Communication command.
This command requires three parameter bytes that exceed the 2-byte parameter encoding space
available in the wIndex field. For this command only, the wValue field will be formatted as 1
command byte and 1 parameter byte. See the command description in Appendix 2 for details.
2. The wLength field is used by the GET COMM CMDS Control command to specify the number of
command/parameter bytes to retrieve from the DS2490 command FIFO; see the command description
for specifics. In all other cases the wLength field is not used and must be set to 0x0000.
The bit-mapped bmRequestType field identifies the characteristics of the USB command per Chapter 9
of the USB Specification. Fields included in this command describe the direction of the transfer, type of
request (core, class, or vendor specific) and the target of the command recipient (device, interface, or
endpoint). The only variation on the bmRequestType field for the different DS2490 vendor-specific
command will be for the transfer direction: host to device, or device to host; the recipient for all
commands will be the device.
The bRequest field contains a 1-byte constant identifying which of the three supported DS2490
command types is being sent. The command constants are defined in Appendix 4 and are summarized as
follows:
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