TMS570LS0432: NHET I2C implementation odd SCL clock wave form

Ken Nadler

Part Number: TMS570LS0432

I have implemented the HET I2C example found in TI's 7485.N2HET_EMU_I2C.ZIP. I am currently running on a Launchpad TMS570LS0432 platform using N2HET[19] as SDA and N2HET[6] as SCL. I modified the example NHET code to use these pins. I don't have the slave chip yet and can only test the master output. Here's where I see something odd. SDA output looks good but the SCL, instead of being a nice square wave is a saw-tooth wave:

In this picture red is the SDL and blue is the SCL.

Here's 7485.N2HET_EMU_I2C.ZIP: 6567.N2HET_EMU_I2C.ZIP

Thanks!

ken

over 7 years ago

0 Sunil Oak over 7 years ago

TI__Mastermind 49120 points

Ken,

Do you have the open-drain mode enabled for the signals you chose for the SCL and SDA? You need an external pull-up per the I2C spec to pull the signal up to 3.3V as the MCU will only drive a low. The pull strength defines how fast the signal gets pulled up. Also, the SDA may not have been configured to be an open-drain output in your case.

Regards,
Sunil

0 Ken Nadler over 7 years ago in reply to Sunil Oak

Intellectual 640 points

Sunil:

Thanks for your reply. I'll look into that. As of now I have the internal pull ups but not the external pull up resistors. Yes, the pins are configured for open drain.

ken

0 Ken Nadler over 7 years ago in reply to Ken Nadler

Intellectual 640 points

Sunil:

Yup, that did it. Adding the external pull-up and the wave looks perfect.

Thanks!

ken

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TMS570LS0432: NHET I2C implementation odd SCL clock wave form