Philips Semiconductors

Product data

PCA9531

2003 Nov 10

5

DEVICE ADDRESSING

Following a START condition the bus master must output the

address of the slave it is accessing. The address of the PCA9531 is

shown in Figure 4. To conserve power, no internal pullup resistors

are incorporated on the hardware selectable address pins and they

must be pulled HIGH or LOW.

1

1

0

0

A2

A1

A0

SLAVE ADDRESS

su01420

FIXED

HARDWARE SELECTABLE

R/W

Figure 4. Slave address

The last bit of the address byte defines the operation to be

performed. When set to logic 1 a read is selected while a logic 0

selects a write operation.

CONTROL REGISTER

Following the successful acknowledgement of the slave address,

the bus master will send a byte to the PCA9531 which will be stored

in the Control Register.

0

0

AI

B2

B1

B0

0

SW01034

0

AUTO-INCREMENT FLAG

REGISTER ADDRESS

RESET STATE: 00h

Figure 5. Control register

CONTROL REGISTER DEFINITION

B2

B1

B0

REGISTER

NAME

TYPE

REGISTER

FUNCTION

0

0

0

INPUT

READ

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

LED0-LED3

SELECTOR

1

1

0

LS1

READ/

WRITE

LED4-LED7

SELECTOR

REGISTER DESCRIPTION

The lowest 3 bits are used as a pointer to determine which register

will be accessed.

If the auto-increment flag is set, the three low order bits of the

Control Register are automatically incremented after a read or write.

This allows the user to program the registers sequentially. The

contents of these bits will rollover to ‘000’ after the last register is

accessed.

When auto-increment flag is set (AI = 1) and a read sequence is

initiated, the sequence must start by reading a register different from

the input register (B2 B1 B0

0 0 0 0).

Only the 3 least significant bits are affected by the AI flag.

Unused bits must be programmed with zeroes.

INPUT — INPUT REGISTER

bit

7

6

5

4

3

2

1

0

Default

X

X

X

X

X

X

X

X

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

this register will be acknowledged but will have no effect.

PSC0 — FREQUENCY PRESCALER 0

bit

7

6

5

4

3

2

1

0

default

0

0

0

0

0

0

0

0

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

The period of BLINK0

+

(PSC0

) 1)

152

PWM0 — PWM REGISTER 0

bit

7

6

5

4

3

2

1

0

default

1

0

0

0

0

0

0

0

The PWM0 register determines the duty cycle of BLINK0. The

outputs are LOW (LED on) when the count is less than the value in

PWM0 and HIGH (LED off) when it is greater. If PWM0 is

programmed with 00h, then the PWM0 output is always HIGH (LED

off).

The duty cycle of BLINK0 is:

PWM0

256

PSC1 — FREQUENCY PRESCALER 1

bit

7

6

5

4

3

2

1

0

default

0

0

0

0

0

0

0

0

PSC1 is used to program the period of PWM output.

The period of BLINK1

+

(PSC1

) 1)

152

PWM1 — PWM REGISTER 1

bit

7

6

5

4

3

2

1

0

default

1

0

0

0

0

0

0

0

The PWM1 register determines the duty cycle of BLINK1. The

outputs are LOW (LED on) when the count is less than the value in

PWM1 and HIGH (LED off) when it is greater. If PWM1 is

programmed with 00h, then the PWM1 output is always HIGH (LED

off) .

The duty cycle of BLINK1 is:

PWM1

256

LS0 — LED0-3 SELECTOR

LED 3

LED 2

LED 1

LED 0

bit

7

6

5

4

3

2

1

0

default

0

0

0

0

0

0

0

0

LS1 — LED4-7 SELECTOR

LED 7

LED 6

LED 5

LED 4

bit

7

6

5

4

3

2

1

0

default

0

0

0

0

0

0

0

0

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

00 = Output is set Hi-Z (LED off - default)

01 = Output is set low (LED on)

10 = Output blinks at PWM0 rate

11 = Output blinks at PWM1 rate