Rainbow Electronics DS2432 - Manual (Page 21)

PRELIMINARY DS2432
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HARDWARE CONFIGURATION Figure 8
Open Drain
Port Pin
RX = RECEIVE
TX = TRANSMIT
100 Ω
MOSFET
V
PUP
RX
TX
TX
RX DATA
R
PU
5 µA
Typ.
BUS MASTER DS2432 1-Wire PORT
TRANSACTION SEQUENCE
The protocol for accessing the DS2432 via the 1-Wire port is as follows:
•
Initialization
•
ROM Function Command
•
Memory or SHA Function Command
•
Transaction/Data
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 DS2432 is on the bus and is ready to
operate. For more details, see the “1-Wire Signaling” section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the seven ROM function commands that
the DS2432 supports. All ROM function commands are eight bits long. A list of these commands follows
(refer to flowchart in Figure 9):
Read ROM [33h]
This command allows the bus master to read the DS2432’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command should only be used if there is a single slave on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open drain will produce a wired-AND result). The resultant family code and 48-bit serial number
read by the master will be invalid.
Match ROM [55h]
The match ROM command, followed by a 64-bit registration number, allows the bus master to address a
specific DS2432 on a multidrop bus. Only the DS2432 that exactly matches the 64-bit registration
number will respond to the following memory function command. All other slaves will wait for a reset
pulse. This command can be used with a single or multiple devices on the bus.