PCA9550_5 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 05 — 13 October 2008 7 of 26
NXP Semiconductors
PCA9550
2-bit I
2
C-bus LED driver with programmable blink rates
6.4 Pins used as GPIOs
LED pins not used to control LEDs can be used as General Purpose Input/Outputs
(GPIOs).
For use as input, set LEDn to high-impedance (01) and then read the pin state via the
Input register.
For use as output, connect external pull-up resistor to the pin and size it according to the
DC recommended operating characteristics. LEDn output pin is HIGH when the output is
programmed as high-impedance, and LOW when the output is programmed LOW through
the LED selector register (LS0). The output can be pulse-width controlled when PWM0 or
PWM1 are used.
6.5 Power-on reset
When power is applied to V
DD
, an internal Power-On Reset (POR) holds the PCA9550 in
a reset condition until V
DD
has reached V
POR
. At that point, the reset condition is released
and the PCA9550 registers are initialized to their default states, all the outputs in the
OFF state. Thereafter, V
DD
must be lowered below 0.2 V to reset the device.
6.6 External RESET
A reset can be accomplished by holding the RESET pin LOW for a minimum of t
w(rst)
. The
PCA9550 registers and I
2
C-bus state machine will be held in their default states until the
RESET input is once again HIGH.
This input requires a pull-up resistor to V
DD
if no active connection is used.