DS2408 Maxim, DS2408 Datasheet - Page 19

• Manufacturer Part Number: DS2408
• Description: The DS2408 is an 8-channel, programmable I/O 1-Wire® chip
• Manufacturer: Maxim

Figure 11. HARDWARE CONFIGURATION
A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At standard speed the 1-Wire bus
has a maximum data rate of 15.3kbps. Communication speed for 1-Wire devices can be typically boosted
to 142kbps by activating the overdrive mode; however, the maximum overdrive data rate for the DS2408
is 100kbps. The value of the pullup resistor primarily depends on the network size and load conditions.
For most applications the optimal value of the pullup resistor will be approximately 2.2kΩ for standard
speed and 1.5kΩ for overdrive speed.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus
MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low
for more than 16µs (overdrive speed) or more than 120µs (standard speed), one or more devices on the
bus may be reset. With the DS2408 the bus must be left low for no longer than 13µs at overdrive speed to
ensure that none of the slave devices on the 1-Wire bus performs a reset. The DS2408 communicates
properly when used in conjunction with a DS2480B 1-Wire driver and serial port adapters that are based
on this driver chip. When operating the device in overdrive or below 4.5V, some 1-Wire I/O timing
values must be modified (see EC table).
HOST CPU
SIMPLE BUS MASTER
RX
TX
SERIAL
PORT
DS2480B BUS MASTER
OPEN-DRAIN
SERIAL OUT
SERIAL IN
PORT PIN
VDD
POL
RXD
TXD
DS2480B
GND
VPP
1-W
V
NC
R
PUP
RX = RECEIVE
TX = TRANSMIT
PUP
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SEE
TEXT
+5V
TO 1-Wire DATA
DATA
DS2408 1-Wire PORT
100Ω
MOSFET
RX
TX
DS2408