Rainbow Electronics MAX6948B - Manual (Page 22)

High-Efficiency PWM LED Driver with Boost
Converter and Five Constant-Current GPIO Ports
22
MAX6948B
Figure 9. START and STOP Conditions
Figure 10. Bit Transfer
Serial Interface
Figure 8 shows the 2-wire serial-interface timing details.
Serial Addressing
The MAX6948B operates as a slave that sends and
receives data through an I
2 C-compatible 2-wire inter-
face. The interface uses a serial-data line (SDA) and
a serial-clock line (SCL) to achieve bidirectional com-
munication between master(s) and slave(s). A master
(typically a microcontroller) initiates all data transfers to
and from the MAX6948B and generates the SCL clock
that synchronizes the data transfer.
The MAX6948B’s SDA line operates as both an input and
an open-drain output. A pullup resistor, typically 4.7kI, is
required on SDA. The MAX6948B’s SCL line operates only
as an input. A pullup resistor is required on SCL if there are
multiple masters on the 2-wire interface, or if the master in a
single-master system has an open-drain SCL output.
Each transmission consists of a START condition (Figure
9) sent by a master, followed by the MAX6948B 7-bit
slave address plus R/W bit, a register address byte, 1 or
more data bytes, and finally a STOP condition.
START and STOP Conditions
Both SCL and SDA remain high when the interface is not
busy. A master signals the beginning of a transmission
with a START (S) condition by transitioning SDA from high
to low while SCL is high. When the master has finished
communicating with the slave, it issues a STOP (P) con-
dition by transitioning SDA from low to high while SCL is
high. The bus is then free for another transmission.
Bit Transfer
One data bit is transferred during each clock pulse
(Figure 10). The data on SDA must remain stable while
SCL is high.
Figure 8. 2-Wire Serial-Interface Timing Details
SCL
SDA
t R t F
t BUF
START
CONDITION
STOP
CONDITION
REPEATED START CONDITION START CONDITION
t SU, STO
t HD, STA
t SU, STA
t HD, DAT
t SU, DAT
t LOW
t HIGH
t HD , STA
SDA
SCL
START
CONDITION
STOP
CONDITION
S P
SDA
SCL
DATA LINE STABLE;
DATA VALID
CHANGE OF DATA
ALLOWED