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TCA9535: Port configuration and settings don't work as expected

Luca Riva
Prodigy 20 points
Part Number: TCA9535
Other Parts Discussed in Thread: PCF8575

Hi,

I am writing because I developed a board with an Atmega1284p processor communicating to two TCA9535RTWR via I2C.

The power supply is 5V through a 100nF capacitor.

On one port expander A0, A1 and A2 are set to GND so that the I2C address is 0x20, on the other one they are set as A0=5V and A1 and A2 are set to GND so that the I2C address is 0x21.

The SCL and SDA are pulled-up correctly and connected to the Atmega processor.

I am programming it with arduino SW. The hardware seems to work correctly.

In fact if I use the following code to program P17-P10 it seem work as expected:

Wire.beginTransmission(byte(0x20));
Wire.write(byte(0x07));
Wire.write(byte(0x17));//P17-P10 0001 0111 (set P17-P15 and P13 as output)
Wire.endTransmission();

Wire.beginTransmission(byte(0x20));
Wire.write(byte(0x03));
Wire.write(byte(0xFF));//P17-P10 1111 1111 (set output to HIGH)
Wire.endTransmission();

Wire.beginTransmission(byte(0x20));
Wire.write(byte(0x03));
Wire.write(byte(0x00));//P17-P10 0000 0000 (set output to LOW)
Wire.endTransmission();

In fact I can see the Led blinking correctly.

The problem appears when I try to configure and set the outputs with ports P07-P00 because I cannot set them HIGH and LOW as for P17-P10:

Wire.write(byte(0x06));//to configure the ports

Wire.write(byte(0x02));//to set the outputs

Another problem is that if I try to read the config registers (or any other register from 0x02 to the last one) with the following code, I always can see only the content of the input registers:

Wire.beginTransmission(byte(0x20));
Wire.write(byte(0x06));
Wire.requestFrom(byte(0x20), uint8_t(2));
IBuffer[0] = Wire.read();
Serial.print("Config 20 0: ");
Serial.println(IBuffer[0], BIN);
IBuffer[0] = Wire.read();
Serial.print("Config 20 1: ");
Serial.println(IBuffer[0], BIN);
Wire.endTransmission();

It seems that the reading instruction works well but the "Wire.write(byte(0x06));" instruction doesn't work and it read from the beginning (reg. 0x00 -> input)

I have the exact same issue with the other port expander (0x21) and also on other boards.

I tried with MAX7311ATG+ from Analog Devices Inc./Maxim Integrated and all work as expected.

Thank you very much.

Best regards

Luca Riva

  • 0
    Guru 316920 points

    Please show an oscilloscope or logic analyzer trace of the failing I²C requests.

    Does your library have the four-parameter form of requestFrom?

    Wire.requestFrom(0x20, 2, 0x06, 1);

  • 0
    TI__Guru 73181 points

    Wire.beginTransmission(byte(0x20));
    Wire.write(byte(0x06));
    Wire.requestFrom(byte(0x20), uint8_t(2));

    ^I haven't tried this kind of transaction in Arduino but shouldn't you end the trans action after you do a wire.write? Otherwise you do a repeated start condition instead of initializing a stop condition on the I2C bus. 

    I think your line should be something like:

    Wire.beginTransmission(byte(0x20));//start condition and send I2C write to device address 0x20
    Wire.write(byte(0x06)); //set the device register you want to read from 

    Wire.endTransmission(); //initiate a stop condition, this allows the state machine of device 0x20h to set the pointer to register 0x06h

    Wire.requestFrom(byte(0x20), uint8_t(2)); //do an I2C read of 2 bytes from device address 0x20h and pull two bytes (from register 0x06h and from 0x07h due to auto-increment)

    Wire.endTransmission(); //initiate a stop condition

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hi Bobby,

    Before opening the post, I also downloaded an Arduino library for TCA port expander.

    In fact it was written as you suggest.

    Wire.beginTransmission(byte(0x20));
Wire.write(byte(0x06));
Wire.endTransmission();
Wire.requestFrom(byte(0x20), uint8_t(2));
IBuffer[0] = Wire.read();
Serial.print("Config 20 0: ");
Serial.println(IBuffer[0], BIN);
IBuffer[0] = Wire.read();
Serial.print("Config 20 1: ");
Serial.println(IBuffer[0], BIN);

    But also with this writing I couldn't read other registers, only input ones.

    Thank you for your reply.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Hi Clemens,

    I'll perform some measure but it is strange that one set of ports work and the other one not.

    Unfortunately my library hasn't four-parameter form of requestFrom. I have first to write which register I want to read and then perform a simply request by setting the number of bytes (as shown in my first post above).

    Thank you for your help.

  • 0 in reply to Luca Riva
    Guru 316920 points

    Please show an oscilloscope or logic analyzer trace of the failing I²C requests.

  • 0 in reply to Luca Riva
    Prodigy 20 points 

    Wire.beginTransmission(byte(0x20));
Wire.write(byte(0x06));
Wire.write(byte(0x00));
Wire.endTransmission();



  • 0 in reply to Luca Riva
    Prodigy 20 points 

      Wire.beginTransmission(byte(0x20));
  Wire.write(byte(0x06));
  Wire.write(byte(0x00));
  Wire.endTransmission();

  Wire.beginTransmission(byte(0x20));
  Wire.write(byte(0x02));
  Wire.write(byte(0xFF));
  Wire.endTransmission();

  Wire.beginTransmission(byte(0x20));
  Wire.write(byte(0x06));
  Wire.endTransmission();
  Wire.requestFrom(byte(0x20), uint8_t(1));

  IBuffer[0] = Wire.read();
  Serial.print("Config 20 0: ");
  Serial.println(IBuffer[0], BIN);

  • 0 in reply to Luca Riva
    Guru 316920 points

    The read transaction indeed returns a value of 0x02.

    The rising edges are very slow; use stronger pull-up resistors, or decrease the frequency.

    Are you sure you actually have TCA9535 chips? Did you get them from an authorized distributor?

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    I'll try.

    The distributor is Digikey or Mouser. We can trust on them.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    I forgot to mention that I tried both 100kHz and 400kHz.

    The other measures have been performed with 400kHz.

    The following one with 100kHz.

    I just modified to 400kHz to see if something changed but the issue is the same with both frequencies.

  • 0 in reply to Luca Riva
    Guru 316920 points

    Is the marking PW535 or PF575(C)?

  • +1 in reply to Luca Riva
    Guru 316920 points

    This is the PCF8575, which has quasi-bidirectional I/Os and no configuration registers.