PCA9544A_4

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 04 — 15 June 2009

7 of 26

NXP Semiconductors

PCA9544A

6.3 Interrupt handling

The PCA9544A provides 4 interrupt inputs, one for each channel and one open-drain

interrupt output. When an interrupt is generated by any device, it will be detected by the

PCA9544A and the interrupt output will be driven LOW. The channel need not be active

for detection of the interrupt. A bit is also set in the control byte. Bits 7:4 of the control byte

correspond to channel 3 to channel 0 of the PCA9544A, respectively. Therefore, if an

interrupt is generated by any device connected to channel 2, the state of the interrupt

inputs is loaded into the control register when a read is accomplished. Likewise, an

interrupt on any device connected to channel 0 would cause bit 4 of the control register to

be set on the read. The master can then address the PCA9544A and read the contents of

the control byte to determine which channel contains the device generating the interrupt.

The master can then reconfigure the PCA9544A to select this channel, and locate the

device generating the interrupt and clear it. The interrupt clears when the device

originating the interrupt clears.

It should be noted that more than one device can be providing an interrupt on a channel,

so it is up to the master to ensure that all devices on a channel are interrogated for an

interrupt.

The interrupt inputs may be used as general purpose inputs if the interrupt function is not

required.

Remark: Several interrupts can be active at the same time. For example: INT3 = 0,

INT2 = 1, INT1 = 1, INT0 = 0, means that there is no interrupt on channel 0 and

channel 3, and there is an interrupt on channel 1 and on channel 2.

Table 4.

Control register: Write—channel selection; Read—channel status

INT3

INT2

INT1

INT0

D3

B2

B1

B0

Command

XXXXX0

Xx

no channel selected

XXXXX

1

0

0

channel 0 enabled

XXXXX

1

0

1

channel 1 enabled

XXXXX

1

1

0

channel 2 enabled

XXX0

X

1

1

1

channel 3 enabled

00000000no channel selected;

power-up default state

Table 5.

Control register read — interrupt

INT3

INT2

INT1

INT0

D3

B2

B1

B0

Command

XXX

0

XXXX

no interrupt on channel 0

1

interrupt on channel 0

XX

0

XXXXX

no interrupt on channel 1

1

interrupt on channel 1

X

0

XXXXXX

no interrupt on channel 2

1

interrupt on channel 2

0

XXXXXXX

no interrupt on channel 3

1

interrupt on channel 3