Question on pin management using PCA9534PW IO Extender

Question

There is an IO expander PCA9534PW, Arduino UNO. I don’t really understand how I can manage this expander using UNO over I2C.

I found an example, but here is the reading mode.

What I need: Set the IO0 pin to exit mode, set the HIGH / LOW level to IO0.

In the datasheet, I just realized that to enter the settings mode - you need to write Wire.write(0x03). How can I do it?

• Mikael Patel: Hint: There is more or less always someone that has done this before you, and shared it. Please see, for instance, github.com/alotaiba/PCA9534.
• Mikael Patel: Answer: Write to the configuration register to set the pin mode. See github.com/alotaiba/PCA9534/blob/master/src/PCA9534.cpp#L14.

Answer 1

You set the pin mode by setting the configuration register.

Wire.beginTransmission(0x20);
Wire.write(0x03); // Configuration Register
Wire.write(0xfe); // IO7-IO1 Input, IO0 Output
Wire.endTransmission();

Then write the output port register with HIGH and LOW.

Wire.beginTransmission(0x20);
Wire.write(0x01); // Output Port Register
Wire.write(0x01); // IO0 HIGH
Wire.endTransmission();
delay(500);
Wire.beginTransmission(0x20);
Wire.write(0x01); // Output Port Register
Wire.write(0x00); // IO0 LOW
Wire.endTransmission();

But using a library is much easier. See, for instance, https://github.com/alotaiba/PCA9534.

• Delta: Many thanks for the example! I have seen this library, but it does not compile under Arduino. github.com/alotaiba/PCA9534/issues/1
• Mikael Patel: It should be very easy to port from Particle. Have you tried to comment out this line, github.com/alotaiba/PCA9534/blob/master/src/PCA9534.h#L14, or just create an empty file with the name "Particle.h".