Datasheet

Any bytes received after the command byte are consid-
ered data bytes. The first data byte goes into the internal
register of the MAX7300 selected by the command byte
(Figure 8). If multiple data bytes are transmitted before
a STOP condition is detected, these bytes are gener-
ally stored in subsequent MAX7300 internal registers
because the command byte address generally autoincre-
ments (Table 4).
Message Format for Reading
The MAX7300 is read using the MAX7300’s internally
stored command byte as address pointer, the same way
the stored command byte is used as address pointer for
a write. The pointer generally autoincrements after each
data byte is read using the same rules as for a write
(Table 4). Thus, a read is initiated by first configuring the
MAX7300’s command byte by performing a write (Figure
7). The master can now read ‘n’ consecutive bytes from
the MAX7300, with the first data byte being read from
the register addressed by the initialized command byte
(Figure 9). When performing read-after-write verification,
remember to reset the command byte’s address because
the stored control byte address generally has been auto-
incremented after the write (Table 4). Table 5 is the regis-
ter address map.
Figure 4. Bit Transfer
Figure 3. Start and Stop Conditions
Figure 2. 2-Wire Serial Interface Timing Details
SDA
SCL
DATA LINE STABLE; DATA VALID
CHANGE OF DATA ALLOWED
SDA
SCL
S
START
CONDITION
P
STOP
CONDITION
SCL
SDA
START CONDITIONSTOP CONDITION
REPEATED START CONDITION
START CONDITION
t
SU, DAT
t
HD, DAT
t
LOW
t
HD, STA
t
HIGH
t
R
t
F
t
SU, STA
t
HD, STA
t
SU, STO
t
BUF
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Maxim Integrated │ 9
MAX7300 2-Wire-Interfaced, 2.5V to 5.5V,
20-Port or 28-Port I/O Expander