Rainbow Electronics MAX3541 - Manual (Page 14)

MAX3541
2-Wire Serial Interface
The MAX3541 use a 2-wire I 2 C-compatible serial inter-
face consisting of a serial-data line (SDA) and a serial-
clock line (SCL). SDA and SCL facilitate bidirectional
communication between the MAX3541 and the master at
clock frequencies up to 400kHz. The master initiates a
data transfer on the bus and generates the SCL signal to
permit data transfer. The MAX3541 behaves as a slave
device that transfers and receives data to and from the
master. Pull SDA and SCL high with external pullup
resistors (1kΩ or greater) for proper bus operation.
One bit is transferred during each SCL clock cycle. A
minimum of nine clock cycles is required to transfer a
byte in or out of the MAX3541 (8 data bits and an
ACK/NACK). The data on SDA must remain stable during
the high period of the SCL clock pulse. Changes in SDA
while SCL is high and stable are considered control sig-
nals (see the
START and STOP Conditions section). Both
SDA and SCL remain high when the bus is not busy.
START and STOP Conditions
The master initiates a transmission with a START condi-
tion (S), which is a high-to-low transition on SDA while
SCL is high. The master terminates a transmission with
a STOP condition (P), which is a low-to-high transition
on SDA while SCL is high.
Acknowledge and Not-Acknowledge Conditions
Data transfers are framed with an acknowledge bit
(ACK) or a not-acknowledge bit (NACK). Both the mas-
ter and the MAX3541 (slave) generate acknowledge
bits. To generate an acknowledge, the receiving device
must pull SDA low before the rising edge of the
acknowledge-related clock pulse (ninth pulse) and
keep it low during the high period of the clock pulse.
To generate a not-acknowledge condition, the receiver
allows SDA to be pulled high before the rising edge of
the acknowledge-related clock pulse, and leaves SDA
high during the high period of the clock pulse.
Monitoring the acknowledge bits allows for detection of
unsuccessful data transfers. An unsuccessful data
transfer happens if a receiving device is busy or if a
system fault has occurred. In the event of an unsuc-
cessful data transfer, the bus master must reattempt
communication at a later time.
Slave Address
The MAX3541 has a 7-bit slave address that must be
sent to the device following a START condition to initi-
ate communication. The slave address is determined
by the state of the ADDR2 and ADDR1 pins and is
equal to 11000[ADDR2][ADDR1]. The eighth bit (R/
W)
following the 7-bit address determines whether a read
or write operation occurs. Table 15 shows the possible
address configurations.
The MAX3541 continuously awaits a START condition
followed by its slave address. When the device recog-
nizes its slave address, it acknowledges by pulling the
SDA line low for one clock period; it is ready to accept
or send data depending on the R/
W bit (Figure 1).
Complete Single-Conversion
Television Tuner
14 ______________________________________________________________________________________
SCL
SDA
1 2 3 4 5 6 7 8 9
S 1 1 0 0 0 ADDR2 ADDR1 R/W ACK
SLAVE ADDRESS
P
NOTE: TIMING PARAMETERS CONFORM WITH I 2 C BUS SPECIFICATIONS.
Figure 1. MAX3541 Slave Address Byte
ADDR2 ADDR1 WRITE ADDRESS READ ADDRESS
0 0 0xC0 0xC1
0 1 0xC2 0xC3
1 0 0xC4 0xC5
1 1 0xC6 0xC7
Table 15. MAX3541 Address Configurations