PCA9551 View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
PCA9551 Datasheet PDF : 21 Pages
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Philips Semiconductors
8-bit I2C LED driver with programmable blink rates
Product data sheet
PCA9551
DEVICE ADDRESSING
Following a START condition the bus master must output the
address of the slave it is accessing. The address of the PCA9551 is
shown in Figure 4. To conserve power, no internal pull-up resistors
are incorporated on the hardware selectable address pins and they
must be pulled HIGH or LOW.
SLAVE ADDRESS
1 1 0 0 A2 A1 A0 R/W
FIXED
HARDWARE SELECTABLE
su01420
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 PCA9551 which will be stored
in the Control Register.
0 0 0 AI 0 B2 B1 B0
RESET STATE: 00h
REGISTER ADDRESS
AUTO-INCREMENT FLAG
Figure 5. Control register
SW01034
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
‘0’ (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.
CONTROL REGISTER DEFINITION
B2
B1
B0
REGISTER
NAME
TYPE
000
INPUT
READ
001
010
011
100
101
110
PSC0
PWM0
PSC1
PWM1
LS0
LS1
READ/
WRITE
READ/
WRITE
READ/
WRITE
READ/
WRITE
READ/
WRITE
READ/
WRITE
REGISTER
FUNCTION
INPUT
REGISTER
FREQUENCY
PRESCALER 0
PWM
REGISTER 0
FREQUENCY
PRESCALER 1
PWM
REGISTER 1
LED0–LED3
SELECTOR
LED4–LED7
SELECTOR
REGISTER DESCRIPTION
INPUT — INPUT REGISTER
LED LED LED LED LED LED LED LED
7
6
5
4
3
2
1
0
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.
NOTE: The default value “X” is determined by the externally applied
logic level, normally ‘1’ when used for directly driving LED with
pull-up to VDD.
PSC0 — FREQUENCY PRESCALER 01
bit
7
6
5
4
3
2
1
0
default 1
1
1
1
1
1
1
1
PSC0 is used to program the period of the PWM output.
The
period
of
BLINK0
+
(PSC0 )
38
1)
NOTE:
1. Prescaler calculation is different between the PCA9551 and
other PCA955x LED Blinkers. A divider ratio of 38 instead of 44
is used. This different divider ratio causes the blinking frequency
to be 13% (1 – 38/44) lower when the same 8-bit word is used.
The programmed value of the FREQUENCY PRESCALER must
be adjusted to compensate for this difference in applications
where the PCA9551 is used in conjunction with other PCA955x
LED Blinkers and the observed blinking frequencies need to be
the same.
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 HIGH (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
256
2004 Oct 01
5
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