Rainbow Electronics DS2406 - Manual (Page 17)

DS2406
17 of 31
TWO-CHANNEL WRITE Figure 10c
1-WIRE
td1
PIO-A
15 µs < td1 < 60 µs 200 ns < td0 < 300 ns
PIO-B
PIO-A
PIO-B
IC=1, SYNCHRONOUS MODE
IC=0, ASYNCHRONOUS MODE
A1 B1 A2 B2 A3 B3 A4 B4
A1 A2 A3 A4
B1 B2 B3 B4
A1 A2 A3 A4
B1 B2 B3 B4
td0
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
DS2406 is a slave device. The bus master is typically a microcontroller. 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 an
open drain or 3-state outputs. The 1-Wire port of the DS2406 is open drain with an internal circuit
equivalent to that shown in Figure 11. Typical bus master ports are shown in Figure 12. If a bi-directional
pin is not available, separate output and input pins can be tied together. A multidrop bus consists of a 1-
Wire bus with multiple slaves attached. The 1-Wire bus has a maximum data rate of 16.3kbits/s. For
normal communication excluding EPROM programming the 1-Wire bus requires only a pull-up resistor
of approximately 5k
W for short line lengths.
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 120µs, one or more of the devices on the bus may be reset. If the 1-Wire bus remains low
for more than 5ms any DS2406 that is not V
CC
powered may perform a power-on reset and switch off
both PIOs.
TRANSACTION SEQUENCE
The sequence for accessing the DS2406 via the 1-Wire port is as follows:
§ Initialization
§ ROM Function Command
§ Memory or Channel Access Function Command
§ Transaction/Data