I2C problem in TCA9539

Question

I am using an STM32F103 and TI's TCA9539 and TCA6408A Port extender. Both of them support 400 kHz (I2C Fastmode) and 100 kHz (I2C standard mode) clock frequencies. I use 3 TCA9539 and 1 TCA6408A. Here is my Schematic diagram:

I use STM32CubeMX and here is the configuration and code:

I tested both 400 kHz mode and 100 kHz mode.

HAL_GPIO_WritePin(TS0_RESET_GPIO_Port, TS0_RESET_Pin, GPIO_PIN_SET);
HAL_GPIO_WritePin(TS1_RESET_GPIO_Port, TS1_RESET_Pin, GPIO_PIN_SET);
HAL_GPIO_WritePin(TS2_RESET_GPIO_Port, TS2_RESET_Pin, GPIO_PIN_SET);
HAL_GPIO_WritePin(TS3_RESET_GPIO_Port, TS3_RESET_Pin, GPIO_PIN_SET);

// ...

while (1) {
  uint8_t test_data[3] = {0x08, 0, 0};
  HAL_I2C_Master_Transmit(&hi2c1, 0X75<<1, test_data, 2,10);
  HAL_I2C_Master_Transmit(&hi2c1, 0X20<<1, test_data, 2,10);
}
// ...

According the datasheet, since I connect the address pin of TCA6408A, the address of it should be 0x20 (7 bits), and the three TCA9539's addresses should be 0x74,0x75 and 0x77. So I sent the test data in the above code.

However, only the TCA6408A responds (ACK), and the TCA9539 doesn't. I changed the different addresses but it doesn't work. Here is the wave:

TCA6408:

TCA9539:

They are all similar devices from TI. I think the only difference between them is that they have different GPIO bits, so I wonder why they have different situations.

Answer 1

In fact the address is wrong. They are 0x74, 0x76 and 0x77, but not 0x75, because A1 is high and A0 is low in the schematic. However there might still be other issues left.

Answer 2

As Justme has pointed out, the addresses of the three TCA9539 in your configuration are 0x74 (A1A0=00), 0x76 (A1A0=10) and 0x77 (A1A0=11.)

The main issue may be the SDA line however, as the scope shot of it looks pretty bad. It may be that the SDA pull-up is not strong enough, or some other connection issue with SDA.

I suggest finding the issue with SDA and square it up before any other troubleshooting. Perhaps start by adding another parallel pull-up resistor to the SDA line and see if the waveform starts to improve.