ESP32 Forum

Hi y'all,
I've been attempting to get SCI communication between a LAUNCHXL-F28379D and an ESP32 working properly, but I'm encountering an issue with synchronizing the transmission. When transmitting between two F28379D chips with a baud rate of 9600, the serial communication works perfectly fine. However, attempting to communicate with an ESP32 using the same configuration does not work. I used an oscilloscope to inspect the signal output from the Rx pins of both chips repeatedly sending 0x55 (alternating low/high) and the signal from the F28379D is slightly out of phase. From the reading, it seems that the frequency is slightly unstable.

I tried changing the starting CPU clock speed, but without any luck:/
I want to sync the PLL-CLK in the esp32 to LAUNCHXL-F28379D which I think should resolve this issue.
The datasheet of esp32 stated that PLL-CLK can be reference to an external crystal for esp32 to run different clock rate.

Any insight if this is going to work, or is there a difference way?

Respectfully,
Yang

Can you post the LA/scope traces? 'Slightly out of phase' sounds weird. Also, what protocol are you using? SCI is pretty general; it's a name for a peripheral that can be used for multiple protocols.

I used Rx pin and Tx pin on the DOIT kit (pin 41 and pin 40), there exist visible delay when both chip are sending the data,
(see attached .gif for reference, the gif is a lot faster than it actually is)

Yellow is the F28379D and Blue is the ESP32,
Both chip are using the same baud rate (9600) and sending the same data.

That looks perfectly fine to me, to be honest. Asynchronous serial communication can easily handle a 1% or so difference in clock speeds, and this seems within that spec. I think your issue is somewhere else. Can you give an example of what you send and how you receive it?

Hi,

The problem is whenever I sent something via Tx (say 80), to Rx pin on the LAUNCHXL-F28379D, I was getting random number in ASCII instead of actual data I sent.

I also tried generated a 10Mhz PWM directly to F28379D Clock input, and syncing them up.
However I'm still getting the same result

Is there something that I might be missing?