
NXP Semiconductors
Table 4.
PCA9553
4-bit I 2 C-bus LED driver with programmable blink rates
Control register de?nition
B2
0
0
0
0
1
1
B1
0
0
1
1
0
0
B0
0
1
0
1
0
1
Register name
INPUT
PSC0
PWM0
PSC1
PWM1
LS0
Type
read
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
LED selector
7.3 Register descriptions
7.3.1 INPUT - Input register
The INPUT register re?ects the state of the device pins. Writes to this register will be
acknowledged but will have no effect.
Table 5.
INPUT - Input register description
Bit
Symbol
Default
7
INPUT[7]
0
6
INPUT[6]
0
5
INPUT[5]
0
4
INPUT[4]
0
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 V DD .
7.3.2 PSC0 - Frequency Prescaler 0
PSC0 is used to program the period of the PWM output.
The period of BLINK0 = (PSC0 + 1) / 44.
Table 6.
PSC0 - Frequency Prescaler 0 register description
Bit
Symbol
Default
7
PSC0[7]
1
6
PSC0[6]
1
5
PSC0[5]
1
4
PSC0[4]
1
3
PSC0[3]
1
2
PSC0[2]
1
1
PSC0[1]
1
0
PSC0[0]
1
7.3.3 PWM0 - Pulse Width Modulation 0
The PWM0 register determines the duty cycle of BLINK0. The outputs are LOW (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 = (256 ? PWM0) / 256.
Table 7.
PWM0 - Pulse Width Modulation 0 register description
Bit
Symbol
Default
7
PWM0
[7]
1
6
PWM0
[6]
0
5
PWM0
[5]
0
4
PWM0
[4]
0
3
PWM0
[3]
0
2
PWM0
[2]
0
1
PWM0
[1]
0
0
PWM0
[0]
0
PCA9553_6
? NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 06 — 29 December 2008
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