Rainbow Electronics DS1957 - Manual (Page 15)

DS1957
15 of 25
HARDWARE CONFIGURATION Figure 5
TTL-EQUIVALENT
PORT PINS
V
DD
STRONG
PULL-UP
DATA IN
DATA OUT
V PUP
BUS MASTER
1.5k Ohms
1-WIRE BUS
TO DS1954
GND
1-WIRE UART
MICROCOMPUTER ACCELERATOR
POWER CONTROL TRUE TIME CLOCK
DS1954 CRYPTO iBUTTON
GND
DATA IN DATA OUT
TRANSACTION SEQUENCE
The sequence for accessing the DS1957 via the 1-Wire port is as follows:
· Initialization
· ROM Function Command
· Data Transfer or Control Function Command
· Read/Write Register/Buffer or Control
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 a presence pulse(s) transmitted by the
slave(s).
The presence pulse lets the bus master know that the DS1957 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 six ROM function commands. All
ROM function commands are eight bits long. A list of these commands follows (refer to flowchart in
Figure 6).