2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port I/O Expander

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9

Any bytes received after the command byte are consid-

ered data bytes. The first data byte goes into the inter-

nal 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

generally stored in subsequent MAX7300 internal regis-

ters because the command byte address generally

autoincrements (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 autoincremented after the write (Table 4). Table 5

is the register address map.

Figure 2. 2-Wire Serial Interface Timing Details

SCL

SDA

START CONDITION

STOP CONDITION

REPEATED START CONDITION

START CONDITION

Figure 3. Start and Stop Conditions

SDA

SCL

S

START

CONDITION

P

STOP

CONDITION

SDA

SCL

DATA LINE STABLE; DATA VALID CHANGE OF DATA ALLOWED

Figure 4. Bit Transfer