Rainbow Electronics DS25LV02 - Manual (Page 10)

DS25LV02: Low-Voltage 1024-Bit EPROM
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than t
LOW0
, slave devices on the bus begin to interpret the low period as a reset pulse, effectively terminating the
transaction.
Figure 4. 1-Wire Bus Interface Circuitry
Vpullup
(1.8 to 5.5V)
Rx
Tx
Rx
Rx = Receive
Tx = Transmit
~100 Ohm
MOSFET
Bus Master Device 1-Wire Port (DQ)
4.7k W
Tx
~0.5µA
TRANSACTION SEQUENCE
The protocol for accessing the DS25LV02 through the 1-Wire port is as follows:
§ Initialization
§ Net Address Command
§ Function Command(s)
§ Data Transfer
All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the
bus master, followed by a presence pulse simultaneously transmitted by the DS25LV02 and any other slaves on
the bus. The presence pulse tells the bus master that one or more devices are on the bus and ready to operate.
For more details, see below.
NET ADDRESS COMMANDS
Once the bus master has detected the presence of one or more slaves, it can issue one of the net address
commands described in the following paragraphs. The name of each Net Address command (ROM command) is
followed by the 8-bit opcode for that command in square brackets.
Read Net Address [33h]. This command allows the bus master to read the DS25LV02’s 1-Wire net address. The
bus master follows the Read Net Address command with 64 read timeslots allowing the 1-Wire slave to transmit its
address. This command can only be used if there is a single slave on the bus. If more than one slave is present, a
data collision occurs when all slaves try to transmit at the same time (open drain produces a wired-AND result).
Match Net Address [55h]. This command allows the bus master to specifically address one DS25LV02 on the
1-Wire bus. Following this command, the bus master transmits the 64 bit net address of the desired slave device.
Only the addressed DS25LV02 responds to any subsequent function command. All other slave devices ignore the
function command and wait for a reset pulse. This command can be used with one or more slave devices on the
bus.
Skip Net Address [CCh]. This command saves time when there is only one DS25LV02 on the bus by allowing the
bus master to issue a function command without specifying the address of the slave. If more than one slave device
is present on the bus, a subsequent function command can cause a data collision when all slaves transmit data at
the same time.
Search Net Address [F0h]. This command allows the bus master to use a process of elimination to identify the
1-Wire net addresses of all slave devices on the bus. The search process involves the repetition of a simple three-