Waveform, UART protocol: missed first start bit

[Kafe]

I am using Waveform 3.13.6 64-bit Qt5.9.7 on a Windows 10. Using the UART protocol decoder, I noticed that the UART protocol decoder does not consider the first bit as a start bit and "loses" the first byte if the trigger starts at the edge of the UART signal. The first two bytes were 0x7e and the picture below shows the problem:

My serial port setting is 115200,8,n,1. I have attached the workspace file.

Please advise me, how can I properly the first byte too. 

Thank you in advance

uart0-for-Digilent-forum.zip

[JColvin]

Hi @Kafe,

The engineer most familiar with the WaveForms software is out on medical leave, but I wanted to let you know that your question has been seen and we will address it when we can. The reason you are encountering what you are is because the trigger is set to an edge rather than a protocol. I know you can set the protocol trigger to hE7[~] on the Receive line in the top right corner of the GUI next to the Position label (you can double click and edit the UART Trigger value), though I do not know if this will properly address your system.

Thanks,
JColvin

[Kafe]

Hi @JColvin,

thank you for your fast response. Hope it is not serious and we will see your engineer soon.

To your advice: I work on project with a small device, which sends binary packets and uses a framing format similar to PPP (frame begin/end is flagged by 0x7e). So my first attempt was set the trigger to protocol (0x7e[~]) with result as follows:

 As you can see the first byte disappeared without a trace. With the edge controlled trigger, I could better analyze the problem.

Regards,

Kafe
 

 

[attila]

Hi @Kafe

Notice that in your capture the trigger position (T0) is on the left of the screen.
The T0 for such protocol value trigger is when it receives the 8th bit, 7.5bit sampling point.
You are visualizing the data after the last bit is received, more exactly staring with the last half bit.

Move the trigger position to the right a bit:

[Kafe]

Hi Attila,

thank you for your advice, it solved all my problem.

Regards,

Kafe