PCA9539: PCA9539

What are the voltages you measure at pins 2, 3, 21, and 24?

Can you show the I²C access on an oscilloscope?

Hi Clemens,

Thank you for your support, please check below reply:
Voltages at pins 2 & 21----0V, pin3---3.7V, pin24--5V

We soldered wires below marked points and captured on logic analyzer waveform

please suggest working code and configuration settings(SDA,SCL & RST) pins---I2C interface.

What is the processor's I/O voltage? Where does the 3.7 V on the reset line come from?

Hi Prabhu,

The /RESET voltage is 3.7 V. This should not trigger a reset condition but the voltage is quite LOW. What voltage supplies are being used in the schematic. I see 5V logic, but it seems that the /RESET pin is pulled to something else. 

Can you confirm that the SDA/SCL waveforms measured at the MCU are the same waveforms appearing at the PCA9539? 

Regards,

Tyler

Hi Clemens,
Processor IO voltage is 5V.
Please check RST pin pullup with 10K--5V

Hi Tyler,

RST pin pullup with 10K--5V

Can you confirm that the SDA/SCL waveforms measured at the MCU are the same waveforms appearing at the PCA9539? 

Both side same waveforms appearing.

The /RESET pin voltage is wrong. There should be nothing that pulls down this line. Do you have any pull-down resistors? Check for solder bridges.

If the /RESET voltage is wrong, then the SDA/SCL voltages also might be wrong. Please use an oscilloscope.

Hi Clemens,

Both sides MCU & IO Expander side we are using 5VCC.

There is no pulldown resistor on /RST pin

What is the voltage on SCL/SDA & /RST pins ?

Hi Clemens,

still we are facing issue on : Slave is not giving Acknowledge.

Hi Prabhu,

I know the SPICE model looks to be accurate and that you are using the DGV package, but can you double check that the pinouts are all the same? 

The square QFN and leaded packaging styles use different pinouts. 

Any update on any solder bridges on the PCB? Do you have a picture of the PCB? 

Do you have any analog waveforms of the signal? Can you use an oscilloscope rather than digital analyzer? It will help give a better picture of what is actually going on at the IO expander. 

Regards,

Tyler