Verify that the data received by Uart

pilar · Joined: 30 Jan 2008 Posts: 197

Hi, I am receiving data through the Uart, but sometimes I receive garbage, I need to verify that the data received are ascii (0-9, A-F) and are different, discard them, how could I do this?

Thank you...

Ttelmah · Joined: 11 Mar 2010 Posts: 19496

Look in the manual for 'is_among', and it's associated functions.

Either setup your own string for the characters you want, or use one of the supplied variants (is_alnum etc.). If this returns 'false', reject the character.

temtronic · Posted: Fri Feb 03, 2017 5:46 pm

hmm 'sometimes garbage'....

Are you using the internal oscillator AND a fast baud rate ? It could be the timing is off just a tad..

Jay

benoitstjean · Posted: Sat Feb 04, 2017 7:53 am

Your explanation is very vague. Post a specific example of what is being transmitted, what you are expecting to receive from that transmission and what is actually being recieved.

Given that you haven't provided much details, how can you determine if 0-9 and A-F isn't garbage as well? Garbage is random therefore random can be anything, including what you're actually looking for. So how will you know that the data received is valid or not? Again, without any details on your scenario, it's somewhat impossble to troubleshoot.

You also haven't specified the UART speed you are using, its configuration as well as your device's crystal/clock speed, CCS version and PIC type.

Also perhaps clock is not the ideal speed for a perfect UART calculation and eventually the UART is out of sync.

Ben

temtronic · Posted: Sun Feb 05, 2017 6:20 am

You don't say where the data is coming from but I'd use PC running a terminal program to look at the 'data'. That way it will confirm/deny that the 'data' actually being sent is 100% correct.
I've got a 15 year old PC running Win98SE and it's sole purpose is doing that. NOTHING else on the PC...no internet, no games,noexcell, etc. Just the terminal program...and QB45.

With 'random garbage' you have to systematically debug, confirm this works, that doesn't....
..otherwise you'll spend hours or days and THEN discover...oops, forgot to conent the cable up to the correct comport...

Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19496

Lets take a deep breath, and 'step back.

For a standard serial connection, data should almost never be anything other than what is sent. For 99.999% of the time.

Now, if you are seeing 'garbage' then the big problem first is understanding 'why'.

Then simply rejecting anything other than hex, won't really be helpful. Problem is that as benoitstjean says, if the garbage is 'random', then it is equally likely to be accepted by a test for 0-9 and A-F, as rejected. So (for instance), '1' gets added, and a '1' gets turned into a '2'. It'll still be accepted, but will be wrong data.

Now there is a test in the 'isamong' suite for 'isxdigit', which tests that a character is a hex digit. This is useful if (for instance), you want to find the part of a message that contains the hex numbers, but the point being made is that if you are genuinely seeing 'garbage', you need to find 'why', before trying to filter the characters....