Datasheet

SCL

Start Condition

Data 1 Valid

SDA

Write to Port

Data Out

From Port

R/W ACK From Slave

ACK From Slave

1 98765432

Data 1

1A20 1S 00 A1 A0 0 A 0000000 A A P

Data to PortCommand ByteSlave Address

SCL

SDA

Data to

Start Condition R/W ACK From Slave ACK From Slave ACK From Slave

1 98765432

Data1/0A20 1S 00 A1 A0 0 A 1000000 A A P

Data to RegisterCommand ByteSlave Address

TCA9554

SCPS233A –NOVEMBER 2011–REVISED MARCH 2012

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Interrupt Output (INT)

An interrupt is generated by any rising or falling edge of the port inputs in the input mode. After time, t

, the

signal INT is valid. Resetting the interrupt circuit is achieved when data on the port is changed to the original

setting; data is read from the port that generated the interrupt. Resetting occurs in the read mode at the

acknowledge (ACK) bit or not acknowledge (NACK) bit after the rising edge of the SCL signal. Interrupts that

occur during the ACK or NACK clock pulse can be lost (or be very short) due to the resetting of the interrupt

during this pulse. Each change of the I/Os after resetting is detected and is transmitted as INT.

Reading from or writing to another device does not affect the interrupt circuit, and a pin configured as an output

cannot cause an interrupt. Changing an I/O from an output to an input may cause a false interrupt to occur if the

state of the pin does not match the contents of the Input Port register.

INT has an open-drain structure and requires a pullup resistor to V

Bus Transactions

Data is exchanged between the master and TCA9554 through write and read commands.

Writes

Data is transmitted to the TCA9554 by sending the device address and setting the least-significant bit to a logic 0

(see Figure 6 for device address). The command byte is sent after the address and determines which register

receives the data that follows the command byte (see Figure 8 and Figure 9). There is no limitation on the

number of data bytes sent in one write transmission.

Figure 8. Write to Output Port Register

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Figure 9. Write to Configuration or Polarity Inversion Registers

Product Folder Link(s): TCA9554