PCA9531_6 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 06 — 19 February 2009 6 of 27
NXP Semiconductors
PCA9531
8-bit I
2
C-bus LED dimmer
6.2 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.
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).
Only the 3 least significant bits are affected by the AI flag. Unused bits must be
programmed with zeroes.
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
logic 1) when used for directly driving LED with pull-up to V
DD
.
Reset state: 00h
Fig 6. Control register
002aac506
0 0 0 AI 0 B2 B1 B0
register address
Auto-Increment flag
Table 3. Register summary
B2 B1 B0 Symbol 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 LED0 to LED3 selector
1 1 0 LS1 read/write LED4 to LED7 selector
Table 4. INPUT - Input register description
Bit 7 6 5 4 3 2 1 0
Symbol LED7 LED6 LED5 LED4 LED3 LED2 LED1 LED0
Default XXXXXXXX
