PCA9685BS NXP [NXP Semiconductors], PCA9685BS Datasheet - Page 24

• Manufacturer Part Number: PCA9685BS
• Description: 16-channel, 12-bit PWM Fm+ I2C-bus LED controller
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
Table 7.
Legend: * default value.
PCA9685_2
Product data sheet
Address Register
FAh
FBh
FCh
FDh
FEh
ALL_LED_ON_L
ALL_LED_ON_H
ALL_LED_OFF_L 7:0 ALL_LED_OFF_L[7:0] W only
ALL_LED_OFF_H 7:5 reserved
PRE_SCALE
ALL_LED_ON and ALL_LED_OFF control registers (address FAh to FEh) bit description
7.3.4 ALL_LED_ON and ALL_LED_OFF control
7.3.5 PWM frequency PRE_SCALE
The ALL_LED_ON and ALL_LED_OFF registers allow just four I
to fill all the ON and OFF registers with the same patterns.
The LEDn_ON and LEDn_OFF counts can vary from 0 to 4095. The LEDn_ON and
LEDn_OFF count registers should never be programmed with the same values.
Because the loading of the LEDn_ON and LEDn_OFF registers is via the I
asynchronous to the internal oscillator, we want to ensure that we do not see any visual
artifacts of changing the ON and OFF values. This is achieved by updating the changes at
the end of the LOW cycle.
The hardware forces a minimum value that can be loaded into the PRE_SCALE register at
‘3’. The PRE_SCALE register defines the frequency at which the outputs modulate. The
prescale value is determined with the formula shown in
where the update rate is the output modulation frequency required. For example, for an
output frequency of 200 Hz with an oscillator clock frequency of 25 MHz:
The PRE_SCALE register can only be set when the SLEEP bit of MODE1 register is set
to logic 1.
prescale value
prescale value
Bit Symbol
7:0 ALL_LED_ON_L[7:0]
7:5 reserved
4
3:0 ALL_LED_ON_H[3:0]
4
3:0 ALL_LED_OFF_H[3:0] W only
7:0 PRE_SCALE[7:0]
ALL_LED_ON_H[4]
ALL_LED_OFF_H[4]
=
=
round
round
Rev. 02 — 16 July 2009
--------------------------------------------------
4096 update_rate
-------------------------- -
4096 200
25 MHz
osc_clock
Access Value
W only
R
W only
W only
R
W only
R/W
16-channel, 12-bit PWM Fm+ I
–
1
0000 0000*
000*
0000 0000*
000*
0001 1110*
=
1*
1*
30
0000*
0000*
–
1
Description
LEDn_ON count for ALL_LED, 8 MSBs
non-writable
ALL_LED full ON
LEDn_ON count for ALL_LED, 4 MSBs
LEDn_OFF count for ALL_LED,
8 MSBs
non-writable
ALL_LED full OFF
LEDn_OFF count for ALL_LED,
4 MSBs
prescaler to program the output
frequency
Equation
2
1:
C-bus write sequences
2
C-bus LED controller
PCA9685
© NXP B.V. 2009. All rights reserved.
2
C-bus, and
24 of 50
(1)
(2)