PCA9550_5

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 05 — 13 October 2008

5 of 26

NXP Semiconductors

PCA9550

6.2.1 Control register definition

6.3 Register descriptions

6.3.1 INPUT - Input register

The INPUT register reflects the state of the device pins. Writes to this register will be

acknowledged but will have no effect.

Remark: The default value ‘X’ is determined by the externally applied logic level (normally

6.3.2 PSC0 - Frequency Prescaler 0

PSC0 is used to program the period of the PWM output.

The period of BLINK0 = (PSC0 + 1) / 44.

6.3.3 PWM0 - Pulse Width Modulation 0

The PWM0 register determines the duty cycle of BLINK0. The outputs are LOW (LED off)

when the count is less than the value in PWM0 and HIGH when it is greater. If PWM0 is

programmed with 00h, then the PWM0 output is always LOW.

The duty cycle of BLINK0 = (256

− PWM0) / 256.

Table 4.

Register summary

B2

B1

B0

Register name

Access

Description

0

0

0

INPUT

read only

input register

0

0

1

PSC0

read/write

frequency prescaler 0

0

1

0

PWM0

read/write

PWM register 0

0

1

1

PSC1

read/write

frequency prescaler 1

1

0

0

PWM1

read/write

PWM register 1

1

0

1

LS0

read/write

LED selector

Table 5.

INPUT - Input register description

Bit

7

6

5

4

3

2

1

0

Symbol

not used

LED1

LED0

Default

000000

X

X

Table 6.

PSC0 - Frequency Prescaler 0 register description

Bit

7

6

5

4

3

2

1

0

Symbol

PSC0[7]

PSC0[6]

PSC0[5]

PSC0[4]

PSC0[3]

PSC0[2]

PSC0[1]

PSC0[0]

Default

11111111

Table 7.

PWM0 - Pulse Width Modulation 0 register description

Bit

7

6

5

4

3

2

1

0

Symbol

PWM0

[7]

PWM0

[6]

PWM0

[5]

PWM0

[4]

PWM0

[3]

PWM0

[2]

PWM0

[1]

PWM0

[0]

Default

10000000