PCA9550_5

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 05 — 13 October 2008

6 of 26

NXP Semiconductors

PCA9550

6.3.4 PSC1 - Frequency Prescaler 1

PSC1 is used to program the period of the PWM output.

The period of BLINK1 = (PSC1 + 1) / 44.

6.3.5 PWM1 - Pulse Width Modulation 1

The PWM1 register determines the duty cycle of BLINK1. The outputs are LOW (LED off)

when the count is less than the value in PWM1 and HIGH when it is greater. If PWM1 is

programmed with 00h, then the PWM1 output is always LOW.

The duty cycle of BLINK1 = (256

− PWM1) / 256.

6.3.6 LS0 - LED selector

The LS0 LED select register determines 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

Table 8.

PSC1 - Frequency Prescaler 1 register description

Bit

7

6

5

4

3

2

1

0

Symbol

PSC1[7]

PSC1[6]

PSC1[5]

PSC1[4]

PSC1[3]

PSC1[2]

PSC1[1]

PSC1[0]

Default

11111111

Table 9.

PWM1 - Pulse Width Modulation 1 register description

Bit

7

6

5

4

3

2

1

0

Symbol

PWM1

[7]

PWM1

[6]

PWM1

[5]

PWM1

[4]

PWM1

[3]

PWM1

[2]

PWM1

[1]

PWM1

[0]

Default

10000000

Table 10.

LS0 - LED selector register description

Bit

7

6

5

4

3

2

1

0

Symbol

LS0[7:4]

LED1

LED0

Default

11110101