9551 查看數據表（PDF） - NXP Semiconductors.

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9551

8-bit I2C-bus LED driver with programmable blink rates

NXP Semiconductors. 

NXP Semiconductors

PCA9551

8-bit I2C-bus LED driver with programmable blink rates

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 ≠ 000).

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

Table 3. Register summary

B2 B1 B0 Symbol

0

0

0

INPUT

0

0

1

PSC0

0

1

0

PWM0

0

1

1

PSC1

1

0

0

PWM1

1

0

1

LS0

1

1

0

LS1

Access

read only

read/write

read/write

read/write

read/write

read/write

read/write

Description

input register

frequency prescaler 0

PWM register 0

frequency prescaler 1

PWM register 1

LED0 to LED3 selector

LED4 to LED7 selector

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.

Table 4.

Bit

Symbol

Default

INPUT - Input register description

7

6

5

4

LED7 LED6 LED5 LED4

X

X

X

X

3

LED3

X

2

LED2

X

1

LED1

X

0

LED0

X

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 VDD.

6.3.2 PSC0 - Frequency Prescaler 0

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 − 38 / 44) lower when the same 8-bit word is used.

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.

PCA9551_8

Product data sheet

Rev. 08 — 31 July 2008

© NXP B.V. 2008. All rights reserved.

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