PCA9551_8

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 08 — 31 July 2008

7 of 26

NXP Semiconductors

PCA9551

6.3.6 LS0 to LS1 - LED selector registers

The LSn LED select registers determine the source of the LED data.

00 = output is set LOW (LED on)

01 = output is set high-impedance (LED off; default)

10 = output blinks at PWM0 rate

11 = output blinks at PWM1 rate

6.4 Pins used as GPIOs

LED pins not used to control LEDs can be used as general purpose I/Os (GPIOs).

For use as input, set LEDn to high-impedance (01) and then read the pin state via the

Input register.

For use as output, connect external pull-up resistor to the pin and size it according to the

DC recommended operating characteristics. LEDn output pin is HIGH when the output is

programmed as high-impedance, and LOW when the output is programmed LOW through

the ‘LED selector’ register. The output can be pulse-width controlled when PWM0 or

PWM1 are used.

6.5 Power-on reset

and the PCA9551 registers are initialized to their default states, all the outputs in the

6.6 External RESET

RESET input is once again HIGH.

Table 9.

LS0 to LS1 - LED selector registers bit description

Legend: * default value.

Register

Bit

Value

Description

LS0 - LED0 to LED3 selector

LS0

7:6

01*

LED3 selected

5:4

01*

LED2 selected

3:2

01*

LED1 selected

1:0

01*

LED0 selected

LS1 - LED4 to LED7 selector

LS1

7:6

01*

LED7 selected

5:4

01*

LED6 selected

3:2

01*

LED5 selected

1:0

01*

LED4 selected