PCA9531 Philips Semiconductors (Acquired by NXP), PCA9531 Datasheet - Page 5

• Manufacturer Part Number: PCA9531
• Description: 8-bit I2C Led Dimmerthe PCA9531 is an 8-bit i C And Smbus I/o Expander Optimized For Dimming Leds in 256 Discrete Steps For Red/green/blue (RGB) Color Mixing And Back Light Applications. The PCA9531 Contains an Internal Oscillator With Two User Progr
• Manufacturer: Philips Semiconductors (Acquired by NXP)

Philips Semiconductors
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.
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.
CONTROL REGISTER DEFINITION
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.
2003 Nov 10
B2
8-bit I
0
0
0
0
1
1
1
RESET STATE: 00h
B1
0
0
1
1
0
0
1
2
C LED dimmer
B0
0
1
0
1
0
1
0
0
1
Figure 5. Control register
Figure 4. Slave address
0
REGISTER
1
FIXED
NAME
INPUT
PWM0
PWM1
PSC0
PSC1
0
LS0
LS1
SLAVE ADDRESS
0
AUTO-INCREMENT FLAG
AI
0
A2
HARDWARE SELECTABLE
0
WRITE
WRITE
WRITE
WRITE
WRITE
WRITE
READ/
READ/
READ/
READ/
READ/
READ/
READ
TYPE
B2
A1 A0
REGISTER ADDRESS
B1
R/W
B0
PRESCALER 0
PRESCALER 1
FREQUENCY
FREQUENCY
REGISTER 0
REGISTER 1
LED0-LED3
LED4-LED7
SELECTOR
SELECTOR
REGISTER
FUNCTION
REGISTER
INPUT
PWM
PWM
SW01034
su01420
5
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.
PSC0 — FREQUENCY PRESCALER 0
PSC0 is used to program the period of the PWM output.
The period of BLINK0 +
PWM0 — PWM REGISTER 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
PSC1 — FREQUENCY PRESCALER 1
PSC1 is used to program the period of PWM output.
The period of BLINK1 +
PWM1 — PWM REGISTER 1
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
LS0 — LED0-3 SELECTOR
LS1 — LED4-7 SELECTOR
The LSx LED select registers determine the source of the LED data.
Default
default
default
default
default
default
default
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
bit
bit
bit
bit
bit
bit
bit
X
7
7
0
7
1
7
0
7
1
7
0
7
0
LED 3
LED 7
X
6
6
0
6
0
6
0
6
0
6
0
6
0
(PSC0 ) 1)
(PSC1 ) 1)
X
5
5
0
5
0
5
0
5
0
5
0
5
0
LED 2
LED 6
152
152
256
256
X
4
4
0
4
0
4
0
4
0
4
0
4
0
3
X
3
0
3
0
3
0
3
0
3
0
3
0
LED 1
LED 5
PCA9531
2
X
2
0
2
0
2
0
2
0
2
0
2
0
Product data
1
X
1
0
1
0
1
0
1
0
1
0
1
0
LED 0
LED 4
0
X
0
0
0
0
0
0
0
0
0
0
0
0