MAX7300 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX7300

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port I/O Expander

Maxim Integrated 

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

28-Port I/O Expander

START CONDITION

SCL

1

2

SDA

BY TRANSMITTER

S

SDA

BY RECEIVER

CLOCK PULSE FOR ACKNOWLEDGMENT

8

9

Figure 5. Acknowledge

SDA

1

0

MSB

SCL

0

A3

A2

A1

A0

R/W

ACK

LSB

Figure 6. Slave Address

Operation with Multiple Masters

If the MAX7300 is operated on a 2-wire interface with

multiple masters, a master reading the MAX7300 should

use a repeated start between the write, which sets the

MAX7300’s address pointer, and the read(s) that takes

the data from the location(s). This is because it is possi-

ble for master 2 to take over the bus after master 1 has

set up the MAX7300’s address pointer, but before

master 1 has read the data. If master 2 subsequently

changes, the MAX7300’s address pointer, then master

1’s delayed read can be from an unexpected location.

Command Address Autoincrementing

Address autoincrementing allows the MAX7300 to be

configured with the shortest number of transmissions

by minimizing the number of times the command

address needs to be sent. The command address

stored in the MAX7300 generally increments after each

data byte is written or read (Table 4).

Initial Power-Up

On initial power-up, all control registers are reset and

the MAX7300 enters shutdown mode (Table 6).

Transition (Port Data Change) Detection

Port transition detection allows any combination of the

seven ports P24–P30 to be continuously monitored for

changes in their logic status (Figure 10). A detected

change is flagged on the transition detection mask reg-

ister INT status bit, D7 (Table 10). If port P31 is config-

ured as an output (Tables 1 and 2), then P31 also

automatically becomes an active-high interrupt output

(INT), which follows the condition of the INT status bit.

Port P31 is set as output by writing bit D7 = 0 and bit

D6 = 1 to the port configuration register (Table 1). Note

that the MAX7300 does not identify which specific

port(s) caused the interrupt, but provides an alert that

one or more port levels have changed.

The mask register contains 7 mask bits that select

which of the seven ports P24–P30 are to be monitored

(Table 10). Set the appropriate mask bit to enable that

port for transition detect. Clear the mask bit if transi-

10 ______________________________________________________________________________________

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