pca9551bs3 NXP Semiconductors, pca9551bs3 Datasheet - Page 5

• Manufacturer Part Number: pca9551bs3
• Description: 8-bit I2c Led Driver With Programmable Blink Rates
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA9551_7
Product data sheet
6.2.1 Control register definition
6.3.1 INPUT - Input register
6.3.2 PSC0 - Frequency Prescaler 0
6.3 Register descriptions
If the Auto-Increment (AI) 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 the 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
Only the 3 least significant bits are affected by the AI flag. Unused bits must be
programmed with zeroes.
Table 3.
The INPUT register reflects the state of the device pins. Writes to this register will be
acknowledged but will have no effect.
Table 4.
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
PSC0 is used to program the period of the PWM output.
The period of BLINK0 = (PSC0 + 1) / 38.
Remark: 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
The programmed value of Frequency Prescaler 0 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.
B2
0
0
0
0
1
1
1
Bit
Symbol
Default
B1
0
0
1
1
0
0
1
Register summary
INPUT - Input register description
LED7
X
B0
0
1
0
1
0
1
0
7
Symbol
INPUT
PSC0
PWM0
PSC1
PWM1
LS0
LS1
Rev. 07 — 23 February 2007
LED6
X
6
8-bit I
LED5
Access
read only
read/write
read/write
read/write
read/write
read/write
read/write
X
5
2
C-bus LED driver with programmable blink rates
38 / 44) lower when the same 8-bit word is used.
LED4
X
4
Description
input register
frequency prescaler 0
PWM register 0
frequency prescaler 1
PWM register 1
LED0 to LED3 selector
LED4 to LED7 selector
LED3
X
3
DD
.
LED2
2
X
PCA9551
© NXP B.V. 2007. All rights reserved.
LED1
000).
X
1
LED0
X
0
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