MAX7302
SMBus/I
2
C Interfaced 9-Port,
Level-Translating GPIO and LED Driver with CLA
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Acknowledge
The acknowledge bit is a clocked 9th bit that the recipi-
ent uses to handshake receipt of each byte of data (see
Figure 13). Thus, each effectively transferred byte
requires 9 bits. The master generates the 9th clock
pulse, and the recipient pulls down SDA during the
acknowledge clock pulse, such that the SDA line is sta-
ble low during the high period of the clock pulse. When
the master is transmitting to the MAX7302, the MAX7302
generates the acknowledge bit because the MAX7302
is the recipient. When the MAX7302 is transmitting to the
master, the master generates the acknowledge bit
because the master is the recipient.
The Slave Address
The MAX7302 has a 7-bit long slave address (Figure
14). The 8th bit following the 7-bit slave address is the
R/W bit. Set R/W bit low for a write command and high
for a read command.
The first 5 bits of the MAX7302 slave address (A6–A2)
are always 1, 0, 0, 1, and 1. Slave address bit A1, A0 is
selected by the address input AD0. AD0 can be con-
nected to GND, V
DD
, SDA, or SCL. The MAX7302 has
four possible slave addresses (see Table 5), and there-
fore, a maximum of four MAX7302 devices can be con-
trolled independently from the same interface.
Message Format for Writing to the MAX7302
A write to the MAX7302 comprises the transmission of the
MAX7302’s slave address with the R/W bit set to zero, fol-
lowed by at least 1 byte of information (see Figure 16).
The first byte of information is the command byte. The
command byte determines which register of the
MAX7302 is to be written to by the next byte, if received.
If a STOP condition is detected after the command byte is
received, the MAX7302 takes no further action beyond
storing the command byte (see Figure 15).
Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register of
the MAX7302 selected by the command byte (see Figure
16). If multiple data bytes are transmitted before a STOP
condition is detected, these bytes are generally stored in
subsequent MAX7302 internal registers because the
command byte address autoincrements (see Table 3).
Message Format for Reading
The MAX7302 is read using the MAX7302’s internally
stored command byte as an address pointer the same
way the stored command byte is used as an address
pointer for a write. The pointer autoincrements after
each data byte is read using the same rules as for a
write. Thus, a read is initiated by first configuring the
MAX7302’s command byte by performing a write
(Figure 15). The master can now read n consecutive
bytes from the MAX7302 with the first data byte being
read from the register addressed by the initialized com-
mand byte (see Figure 17). When performing read-
after-write verification, remember to reset the command
byte’s address because the stored command byte
address has been autoincremented after the write.
