Problem with PCA9535

Chethan,

What is the I2C speed? And what is the amount of time between the interrupt asserting, and the I2C read?

Also can you send us a copy/screenshot of the schematic?

hai.

  I2C is in standard mode(100 khz),after interrupt it will take approximately 6 second,after 6 sec it will send the command and read the data quickly in that time all port pins are high. i tried with fast mode also but it is also same problem. if i disconnect the  interrupt pin just press the key  with rst the controller i will get valid data, if the data read function call  from ISR get delayed to search the address ,

   also i tried with only one expander with controller, please give the solution.

    Please find attached file

Chethan,

I think the problem that you're running into is that you are waiting too long after the interrupt is triggered to read the registers. If you look at the schematic below, you can see that the data on the input pin will cause the interrupt XOR to change, but the data will not be latched until you send the read pulse with an I2C read. 

Try shortening how long it takes to read the register to shortly after the interrupt is flagged to about 50ms to prevent errors in switch bouncing.

This also would explain why you read it correctly if you hold the key for a long time, because the pin is still seeing a logic-low when it sends the read-pulse.

Also if this is going into production, i would suggest the TCA9535 over the PCA version. The TCA version fixes some Power-on-reset issues that are seen in the PCA9535.

 Thank you for your suggestions i will try it in your way...

     Regards 

chethan kumar

Chethan,

Did the suggestion fix your problem?

Ya i solved that problem now its working fine....

Regards

chethan kumar