PCA9550 Philips Semiconductors, PCA9550 Datasheet - Page 4

• Manufacturer Part Number: PCA9550
• Description: 2-bit I2C LED driver with programmable blink rates
• Manufacturer: Philips Semiconductors

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 PCA9550 is
shown in Figure 3. To conserve power, no internal pull-up resistor is
incorporated on the hardware selectable address pin and it 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 PCA9550 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.
2003 May 02
B2
2-bit I
0
0
0
0
1
1
RESET STATE: 00h
B1
0
0
1
1
0
0
2
C LED driver with programmable blink rates
B0
0
1
0
1
0
1
0
1
Figure 4. Control register
REGISTER
Figure 3. Slave address
0
NAME
INPUT
PWM0
PWM1
1
PSC0
PSC1
LS0
0
SLAVE ADDRESS
0
FIXED
AUTO-INCREMENT FLAG
AI
0
0
WRITE
WRITE
WRITE
WRITE
WRITE
0
READ/
READ/
READ/
READ/
READ/
READ
TYPE
B2
0
HARDWARE
SELECTABLE
REGISTER ADDRESS
A0
B1
R/W
PWM REGISTER 0
PWM REGISTER 1
INPUT REGISTER
LED SELECTOR
SW00928
B0
PRESCALER 0
PRESCALER 1
FREQUENCY
FREQUENCY
REGISTER
FUNCTION
SW01034
4
Unused bits must be programmed with zeroes.
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 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 is: 256 – 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 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 is: 256 – PWM1
LS0 — LED SELECTOR
The LSx LED select registers determine the source of the LED data.
default
default
default
default
default
default
00 = Output is set LOW (LED on)
01 = Output is set Hi-Z (LED off - default)
10 = Output blinks at PWM0 rate
11 = Output blinks at PWM1 rate
bit
bit
bit
bit
bit
bit
7
0
7
1
7
1
7
1
7
1
7
1
6
0
6
1
6
0
6
1
6
0
6
1
(PSC0 ) 1)
(PSC1 ) 1)
5
0
5
1
5
0
5
1
5
0
5
1
38
38
4
0
4
1
4
0
4
1
4
0
4
1
256
256
3
0
3
1
3
0
3
1
3
0
3
0
LED 1
PCA9550
2
0
2
1
2
0
2
1
2
0
2
1
Product data
1
X
1
1
1
0
1
1
1
0
1
0
LED 0
0
X
0
1
0
0
0
1
0
0
0
1