Hello NXP community,
I'm facing a weird issue of device not getting detected on i2c bus.
Connection on bus is as follows:
Master: MCU (DSPIC33EP)
Slave: 24LC32A, PCAL6416APW(ADDR 0), PCAL6416APW (ADDR 1)
Currently on PCB:
PCAL6416APW(ADDR 0) i2c bus for this slave has been removed. (jumpers) so only 2 devices are present digital output and eeprom.
When I try to write something on io expander, i always get NACK. Please let me know what is wrong here.
Attaching schematic and Logic analyser plot below:
Input schematic:
output schematic: (please note the ADDR pin is now connected to +5V as mentioned in datasheet pg6)
logic analyser write to output (Address 1).:
Please let me know what is going on here and what I can do to make it work.
Regards,
Macjan
Hi Macjan,
please confirm if you have used pull-up resistors for the SDA and SCL lines to the VDD(I2C) voltage source. Please refer to the Figure 17. in the PCAL6416A datasheet.
If you have used the pull-up resistors, please state the value and approximate length of the SDA and SCL PCB traces and/or Cables.
If you haven't used the pull-up resistors, please test to use 2kOhm, also please state the value and approximate length of the SDA and SCL PCB traces and/or Cables.
With Best Regards,
Jozef
Jozef,
Thank you.
Yes there is a 2.2k Pull up on SCL and SDA line.
Regards,
Macjan
Hi Macjan,
thank you for the additional information. According to your description, everything should work correctly. Please try following.
1. Please disconnect the EEPROM 24LC32A, and leave only the MCU master and the PCAL6416APW (ADDR 1) slave, with the pull-up resistors.
2. Please connect the !INT pin though a 2k2 pull-up resistor to VDD_I2C pin. To the 3.3V source.
Although the !INT is an output, and it shouldn't be a problem, to leave it floating, there is nothing in the datasheet, how it should be connected when unused. Therefore, please connect it as described in the Table 3.
3. Please power on the devices and please try to engage communication between the MCU and the PCAL6416APW (ADDR 1). If you will still receive the NACK from the slave, please do PCAL6416A POR according to the Figure 22. in the section 9.3 in the PCAL6416A datasheet and please try to engage the communication again.
With Best Regards,
Jozef
Hello Josef,
I have removed 20E connected on 24LC32A. Now only one IC is connected to microcontroller on i2c BUS.
This is below waveform:
Observation: The device still does not respond. I'm sending u voltages on each pin for the same in next image.
As per description in datasheet, its mentioned that Voltage on Reset when not used connect to i2c bus voltage (3.3V in this case).
INT is not connected.
ADDR + VDD(P) are connected to 5V
I2C SDA, SCL, RESET, VDD_I2c are connected to 3.3V
20E on i2c bus are removed for EEPROM + IO Expander (PCAL6416)
Only one i2c device is connected at address 0x21
If any thing I need to try pls do let me know.
Hello Josef,
The chip started responding to the commands.
There was no issue with wiring. Problem was that the chip i2c bus was in bit banging mode and this state below caused the address to change to 0x31 instead of 0x21. Please check below:
If you see carefully, the Pulse remains high till next clock pulse, this could easily change address. I just had a doubt about it since it was not responding.
After i modified the code this is the response. It replied immediately. I was always checking logic analyzer bus details below and not pulses. Seeing pulses created the doubt.
Thank you for the support. This resolves my issue.
Regards,
Macjan.
