Rainbow Electronics DS2411 - Manual (Page 4)

DS2411
4 of 11
Note 11: e represents the time required for the pullup circuitry to pull the voltage on I/O up V
IL
to
V
TH
.
Note 12: d represents the time required for the pullup circuitry to pull the voltage on I/O up from
V
IL
to the input-high threshold of the bus master.
Note 13: Interval begins when the voltage drops below V
TL
during a negative edge on I/O and ends
when the voltage rises above V
TH
during a positive edge on I/O.
OPERATION
The DS2411’s registration number is accessed through a single data line. The 48-bit serial number, 8-bit
family code, and 8-bit CRC are retrieved using the Dallas 1-Wire protocol. This protocol defines bus
transactions in terms of the bus state during specified time slots that are bus-master-generated falling
edges on the I/O pin. All data is read and written least significant bit first. The device requires a delay
between V
CC
power-up and initial 1-Wire communication, t
PWRP
(1200 ms). During this time the device
may issue presence-detect pulses.
1-Wire BUS SYSTEM
The 1-Wire bus has a single bus master and one or more slaves. In all instances, the DS2411 is a slave
device. The bus master is typically either a microcontroller or a Dallas Semiconductor bridge chip such as
the DS2480, DS2490, or DS1481. The discussion of this bus system is broken down into three topics:
hardware configuration, transaction sequence, and 1-Wire signaling (signal type and timing).
Hardware Configuration
The 1-Wire bus has a single data line, I/O. It is important that each device on the bus be able to drive I/O
at the appropriate time. To facilitate this, each device has an open-drain or three-state output. The
DS2411 has an open-drain output with an internal circuit equivalent to that shown in Figure 3. The bus
master can have the same equivalent circuit. If a bidirectional pin is not available on the master, separate
output and input pins can be connected together. The bus requires a pullup resistor at the master end of
the bus, as shown in Figure 4. A multidrop bus consists of a 1-Wire bus with multiple slaves attached.
The 1-Wire bus has a maximum data rate of 15.4kbps in standard speed and 125kbps in overdrive.
The idle state for the 1-Wire bus is high. If a transaction needs to be suspended for any reason, I/O must
remain high if the transaction is to be resumed. If the bus is pulled low, slave devices on the bus will
interpret the low as either a timeslot, or a reset depending on the duration.
Figure 1. DS2411 REGISTRATION NUMBER
MSB LSB
8-BIT CRC CODE 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE
(01h)
MSB LSB MSB LSB MSB LSB