PCA9685_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 16 July 2009

13 of 50

NXP Semiconductors

PCA9685

7.3.1 Mode register 1, MODE1

[1]

When the Auto Increment flag is set, AI = 1, the Control register is automatically incremented after a read or write. This allows the user

to program the registers sequentially.

[2]

It takes 500

µs max. for the oscillator to be up and running once SLEEP bit has been set to logic 0. Timings on LEDn outputs are not

guaranteed if PWM control registers are accessed within the 500

µs window. There is no start-up delay required when using the

EXTCLK pin as the PWM clock.

[3]

No PWM control is possible when the oscillator is off.

[4]

When the oscillator is off (Sleep mode) the LEDn outputs cannot be turned on, off or dimmed/blinked.

Table 4.

MODE1 - Mode register 1 (address 00h) bit description

Legend: * default value.

Bit

Symbol

Access

Value

Description

7

RESTART

R

Shows state of RESTART logic. See Section 7.3.1.1 for detail.

W

User writes logic 1 to this bit to clear it to logic 0. A user write of logic 0 will have no

effect. See Section 7.3.1.1 for detail.

0*

Restart disabled.

1

Restart enabled.

6

EXTCLK

R/W

To use the EXTCLK pin, this bit must be set by the following sequence:

1. Set the SLEEP bit in MODE1. This turns off the internal oscillator.

2. Write logic 1s to both the SLEEP and EXTCLK bits in MODE1. The switch is

now made. The external clock can be active during the switch because the

SLEEP bit is set.

This bit is a ‘sticky bit’, that is, it cannot be cleared by writing a logic 0 to it. The

EXTCLK bit can only be cleared by a power cycle or software reset.

EXTCLK range is DC to 50 MHz.

0*

Use internal clock.

1

Use EXTCLK pin clock.

5

AI

R/W

0*

Register Auto-Increment disabled[1].

1

Register Auto-Increment enabled.

4

SLEEP

R/W

0

Normal mode[2].

1*

Low power mode. Oscillator off[3][4].

3

SUB1

R/W

0*

1

2

SUB2

R/W

0*

1

1

SUB3

R/W

0*

1

0

ALLCALL

R/W

0

1*

refresh_rate

EXTCLK

4096

prescale

1

+

()

×

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