PmodAD2 is having low voltage

[LucasFroze]

Hi Digilent Masters, 

 

I'm starting to work on a mini project which reading back PmodAD2 VinX data from Arria 10 FPGA dev kit through I2C interface.

I'm using Quartus to develop the code, and enabled weak pull up resistor on both SCL & SDA in Quartus

The Vcc is connected with 5V and Vin1 - Vin4 are connected with inputs which have max 1.8V.

When I measure my SCL with DMM, it shows only 1.4V when HIGH and drops to 0.3 when SCL goes LOW. From the PmodAD2 schematics, it tells me this is definitely not meeting the requirements.

What did I do wrong?

FYI, I'm new to FPGA design

Would be appreciated if anyone can offer their insights on this issue.

 

Regards,

Lucas Kang

[JColvin]

Hi @LucasFroze,

I'm not sure what the issue might be; I don't know what the Arria 10 FPGA kit has it's own pullup resistors for the I2C or what those values are which you enabled.

I know from the output low voltage on the AD7991, https://www.analog.com/media/en/technical-documentation/data-sheets/AD7991_7995_7999.pdf, has a maximum output value of 0.4 V or 0.6 V depending on what current sink value is, so it's technically within limits though I don't know why it's measuring that high of a voltage on a logic low level. Similarly the logic level high is less than expected though within limits. Regardless, I'm not sure why it's not going between 0V for logic low and 1.8 V for logic high.

Thanks,
JColvin