Philips Semiconductors

Product data

PCA9545

2002 Mar 28

5

853-2302 27311

INTERRUPT HANDLING

The PCA9545 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 PCA9545 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.

Bits 4 – 7 of the control register correspond to channels 0 – 3 of the

PCA9545, 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 PCA9545 and read the contents of the control

register to determine which channel contains the device generating the

interrupt. The master can then reconfigure the PCA9545 to select this

channel, and locate the device generating the interrupt and clear it.

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.

pull-up resistor.

Table 2. Control Register Read — Interrupt

INT3

INT2

INT1

INT0

B3

B2

B1

B0

COMMAND

X

X

X

0

X

X

X

X

No interrupt

on channel 0

X

X

X

1

X

X

X

X

Interrupt on

channel 0

X

X

0

X

X

X

X

X

No interrupt

on channel 1

X

X

1

X

X

X

X

X

Interrupt on

channel 1

X

0

X

X

X

X

X

X

No interrupt

on channel 2

X

1

X

X

X

X

X

X

Interrupt on

channel 2

0

X

X

X

X

X

X

X

No interrupt

on channel 3

1

X

X

X

X

X

X

X

Interrupt on

channel 3

NOTE: Several interrupts can be active at the same time.

Ex: INT3 = 0, INT2 = 1, INT1 = 1, INT0 = 0, means that there is no

interrupt on channels 0 and 3, and there is interrupt on channels 1

and 2.

RESET INPUT

The RESET input is an active-LOW signal which may be used to

recover from a bus fault condition. By asserting this signal LOW for

machine and will deselect all channels. The RESET input must be

POWER-ON RESET

point, the reset condition is released and the PCA9545 registers and

causing all the channels to be deselected.

VOLTAGE TRANSLATION

The pass gate transistors of the PCA9545 are constructed such that

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

MINIMUM

TYPICAL

MAXIMUM

SW00820

2.0

Figure 5 shows the voltage characteristics of the pass gate

transistors (note that the graph was generated using the data

specified in the DC Characteristics section of this datasheet). In

voltage should be equal to, or lower than the lowest bus voltage. For

example, if the main bus was running at 5 V, and the downstream

2.7 V to effectively clamp the downstream bus voltages. Looking at

PCA9545 supply voltage is 3.5 V or lower so the PCA9545 supply

voltage could be set to 3.3 V. Pull-up resistors can then be used to

bring the bus voltages to their appropriate levels (see Figure 12).

More Information can be found in Application Note AN262

PCA954X