# Baud Rate calculation from logic analyzer

I am somewhat new to approaching this from this angle, been using serial coms as documented for many many years configuring everything from radios to network equipment. Familiar with what baud rate IS but not so certain on how it gets calculated. I have been doing research and it I have seen it referenced as (1/pulse width in microsecond)*(10^6) But it does not matter how about I get this, I always get gibberish in my terminal.

I have tried all the standard increments and figure this has to be something obscure and specific.

I know the data is there and I know it is serial, because my LA (Kingst LA2016) is reading and converting to ASCII, it is forming words and sentences, so the data IS correct.

Using a sample of a completed frame of data /8 or /9 with stop bit, or an individual bit, I am still not getting a functional baud rate.

Using this sample, can someone explain what I am getting wrong here? IF the sample will not give the information, can you detail what I would need to look at show?

Edit: Still working on this, and figured out KingstVis does this math for me, I see that it works it out to 575208, which is awefull close to 576000, but still no joy :/

I do not think it matters but this is wired into pin 3 RX and pin 4 GRD on a "0403:6001 Future Technology Devices International, Ltd FT232 Serial (UART) IC" USB-C cable. Just in case that seems like a culprit...

• Zoom in closer on your logic analyzer so that you can measure the width of a single bit more accurately. [1 / (bit-width) ] is your baud rate. Aug 4, 2023 at 2:25
• Just did that and reposted. I use this serial cable sometimes several times a week, and never had an issue. I even use it from my phone sometimes. So I am hesitant to suspect cable? That gives me 114942 which is awful close to 115200, but no joy there either. Aug 4, 2023 at 2:34
• @Sabre Just to be clear, the logic anayzer shows correct data and baud rate can be guessed to be 115200, but where are you plugging the logic analyzer, and are you feeding that same signal into USB adapter? Is the USB adapter you have a USB-to-TTL adapter with wires or USB-to-RS232 adapter with DE9 connector? There is a big difference. Aug 4, 2023 at 5:35
• I'm sure it's 115200. To reduce measurement inaccuracy, I commonly count 10 bits and use that interval. -- BTW, you added some important information in comments below the first answer. Please edit your question and add it there. Comments are too easily overseen. Aug 4, 2023 at 5:36
• @Sabre I bet the logic analyzer can't determine if the voltage levels are RS-323 or something else. The protocol should not be called RS-232 because it's not something it defines. That's just logic level UART protocol, sometimes called asynchronous start stop protocol. Aug 4, 2023 at 17:22

You have the incorrect cable for what you are trying to do.

That's an RS-232 cable you are using.

It needs RS-232 voltage levels on input.

You are giving it a logic level signal.

The RS-232 levels are also inverted in comparison to logic levels.

So, you either need a different cable without RS-232 levels, or, you need a RS-232 transceiver board to convert your logic level signals to RS-232 levels.

• Ahh, this makes some sense. Suggestions? Something like this? digikey.com/en/products/detail/sparkfun-electronics/DEV-09873/… Aug 4, 2023 at 17:55
• Asking for suggestions, what to buy and from where, are off topic. Any logic level (non-RS232) USB to UART chip device/module/cable may work for you as long as it uses the same logic voltage levels as the device you are connecting to. Aug 4, 2023 at 17:59
• 10:4 I will do some research. Thanks for the lead, they are cheap, so will just get one and try, will report back. Aug 4, 2023 at 18:57
• So ordered a 1.8v, 3.3v, 5v USB - TTL adapter, should know next week if this is purely a voltage issue, and not BAUD rate issue. :-) Aug 5, 2023 at 19:00
• You were absolutely correct, after some research this was suspected to be a logic level issue, learn.sparkfun.com/tutorials/logic-levels and a a new interface, still reports "Future Technology Devices International, Ltd FT232 Serial (UART) IC" but is adjustable 0-5 volts. This new interface reads it at 115200 like a dream set to 3.3v. Many thanks! Aug 9, 2023 at 0:35

I have seen it referenced as (pulse width in microsecond / 10)*(6^10) But it does not matter how about I get this, I always get gibberish in my terminal.

Baud rate is the number symbols transferred per second. Therefore if the pulse width is longer the baud rate should be lower, not higher.

A more plausible formula is

$$B = \frac{1}{T_s}$$

where $$\B\$$ is baud rate and $$\T_s\$$ is the symbol duration (what you call pulse width) in seconds.

The main point is the symbol duration or pulse width should be in the denominator not the numerator. The other factor in your formula (you wrote "6^10" but you probably meant $$\10^6\$$ is just to convert from microseconds to seconds.

In your sample the symbol period is about 10 us, so the baud rate is about 100 kbaud. The nearest common UART rate is 115.2 kbaud, so I'd start there.

• You are correct I typed wrong on my phone on the way to dinner, I just got back to computer and checked, I tried (1/10)*(10^6) and came up with 100000, which result din gibberish, so I tried 115200, gibberish. so I tried 1/9.5, 1/10.5, 1/11, just in case I was slightly off. Does it have to be to the digit exact? KingstVis exports as both CSV and BIN, I tried importing into sigrok to see if I could get more precise calculations, no go. The LA2016 is collecting in 5s intervals at 200Mhz. Aug 3, 2023 at 23:51
• I do not think it matters but this is wired into pin 3 RX and pin 4 GRD on a "0403:6001 Future Technology Devices International, Ltd FT232 Serial (UART) IC". cable .Just in case that seems like a culprit... Aug 4, 2023 at 2:14
• @Sabre, I'm pretty sure you've got the baud rate correct at 115.2 kbaud. Try looking at other settings like start/stop bits, parity bits, etc. Aug 4, 2023 at 2:48
• Any way to glean that or trial and error? The analyzer decodes the data, so I assume it is determining this somehow? Aug 4, 2023 at 2:57
• @Sabre, your trace looks to me like 1 start bit, no parity. But I don't work with serial data much. Aug 4, 2023 at 3:13