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Product data sheet

Rev. 03 — 3 March 2005

7 of 27

Philips Semiconductors

PCA9545A

7.2.2 Interrupt handling

The PCA9545A 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

PCA9545A and the interrupt output will be driven LOW. The channel does not need to be

active for detection of the interrupt. A bit is also set in the control register.

Bit 4 through bit 7 of the control register corresponds to channel 0 through channel 3 of

the PCA9545A, respectively. Therefore, if an interrupt is generated by any device

connected to channel 1, 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 PCA9545A and read the contents of the control register to determine

which channel contains the device generating the interrupt. The master can then

reconfigure the PCA9545A to select this channel, and locate the device generating the

interrupt and clear it.

It should be noted that more than one device can provide 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. Example: INT3 = 0, INT2 = 1,

INT1 = 1, INT0 = 0, means that there is no interrupt on channel 0 and channel 3, and

there is interrupt on channel 1 and channel 2.

7.3 RESET input

The RESET input is an active LOW signal which may be used to recover from a bus fault

Table 5:

Control register: Read—interrupt

INT3

INT2

INT1

INT0

B3

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