DS2409 Dallas Semiconducotr, DS2409 Datasheet - Page 9

• Manufacturer Part Number: DS2409
• Description: MicroLAN Coupler
• Manufacturer: Dallas Semiconducotr

HARDWARE CONFIGURATION Figure 6
1-WIRE BUS SYSTEM
The 1-Wire bus is a system which has a single bus master and one or more slaves. In all instances the
DS2409 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware
configuration, transaction sequence, and 1-Wire signaling (signal types and timing). A 1-Wire protocol
defines bus transactions in terms of the bus state during specified time slots that are initiated on the
falling edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter
4 of the Book of DS19xx iButton Standards.
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to
drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open
drain or 3-state outputs. The 1-Wire input of the DS2409 is open drain with an internal circuit equivalent
to that shown in Figure 6. A multidrop bus consists of a 1-Wire bus with multiple slaves attached. The 1-
Wire bus has a maximum data rate of 16.3k bits per second and requires a pullup resistor of
approximately 1.5k? or a DS2480 driver for MicroLAN applications.
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 120 µs, one or more of the devices on the bus may be reset. The DS2409 may perform a
power-on reset cycle and deactivate both 1-Wire outputs if the 1-Wire input is low for minimum 8 ms. A
low time of 12 ms or more will always cause a power-on reset cycle.
Transaction Sequence
The protocol for accessing the DS2409 via the 1-Wire port is as follows:
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the
slave(s). The presence pulse lets the bus master know that the DS2409 is on the bus and is ready to
operate. For more details, see the “1-Wire Signaling” section.
Initialization
ROM Function Command
Control Function Command
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