PCA9501 datasheet(7/28 Pages) NXP

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PCA9501_4

Product data sheet

Rev. 04 — 10 February 2009

7 of 28

NXP Semiconductors

PCA9501

8-bit I2C-bus and SMBus I/O port with interrupt, 2-kbit EEPROM

7.3.1 Quasi-bidirectional I/Os

A quasi-bidirectional I/O can be used as an input or output without the use of a control

signal for data direction. At power-on the I/Os are HIGH. In this mode, only a current

source to VDD is active. An additional strong pull-up to VDD allows fast rising edges into

heavily loaded outputs. These devices turn on when an output is written HIGH, and are

switched off by the negative edge of SCL. The I/Os should be HIGH before being used as

inputs. See Figure 9.

7.3.2 Interrupt

The PCA9501 provides an open-drain output (INT) which can be fed to a corresponding

input of the microcontroller. This gives these chips a type of master function which can

initiate an action elsewhere in the system. See Figure 10.

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

After time tv(INT) the signal INT is valid. See Figure 11.

Resetting and reactivating the interrupt circuit is achieved when data on the port is

changed to the original setting or data is read from or written to the port which has

generated the interrupt.

Resetting occurs as follows:

• In the Read mode at the acknowledge bit after the rising edge of the SCL signal

• In the Write mode at the acknowledge bit after the HIGH-to-LOW transition of the SCL

signal

• Returning of the port data to its original setting

• Interrupts which occur during the acknowledge clock pulse may be lost (or very short)

due to the resetting of the interrupt during this pulse.

Each change of the I/Os after resetting will be detected and, after the next rising clock

edge, will be transmitted as INT. Reading from or writing to another device does not affect

the interrupt circuit.

Fig 9.

Transient pull-up current (IOHt) while IO3 changes from LOW to HIGH and back to LOW

slave address (I/O expander)

START condition

R/W

acknowledge

from slave

002aad292

data to port

acknowledge

from slave

12345678

SCL

SDA

IO3 output voltage

IO3 pull-up output current

acknowledge

from slave

data to port

A5 A4 A3 A2 A1 A0

IO3

STOP

condition

IO3

IOHt

IOH

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