Baudrate 9600 problem

atmega64 · Joined: 23 Feb 2005 Posts: 298 Location: ITALY

Hi,
I use an atmega1284 with a 16Mhz oscillator ..
if I use a baud rate of 9600, I have problems receiving the first character sent ... why?

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

I would suspect that using ischarwaiting together with waitkey is the problem, at the least, one of them is redundant.

You do bufferend input, so IsCharWaiting tells you at least one character is in the buffer. Then just read it with inkey, you dont need to use waitkey, you already know there is a character there.

Depending on what you want to do, I find its usually better to put ischarwaiting in a loop, so it keeps adding characters to your output string untill the buffer is empty. At some point you get an end of line character, or carriage return, use that to determine when to output the completed string to the display.

atmega64 · Joined: 23 Feb 2005 Posts: 298 Location: ITALY

ok thanks…

but With "waitms 2" it works

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

both inkey and waitkey can be used in combination with ischarwaiting.
The waitms is indeed not needed.

The provided info given is not complete : we have no idea when the data is sent. Is the code running before the data is sent? And exactly what data is sent? En how much, etc.

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

Thanks for the clarification Mark. I thought that waitkey might be waiting for the next character, after the one which set the ischarwaiting flag. In which case that one would be missed.

atmega64 · Joined: 23 Feb 2005 Posts: 298 Location: ITALY

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

I do not know what the goal of the code is?
It looks odd. There is no trailing character to check? Like a CR or LF ?
Usually you signal the end of a data stream with a trailing character like CR + LF or one of them.

your code seems to grab some data and when no data is available it resets.

so this is how it usually works :

MWS · Joined: 22 Aug 2009 Posts: 2262

atmega64 · Joined: 23 Feb 2005 Posts: 298 Location: ITALY

EDC · Joined: 26 Mar 2014 Posts: 971

I never saw CCTALK protocol so I read Wikipedia https://en.wikipedia.org/wiki/CcTalk

I make quick test on the simulator

atmega64 · Joined: 23 Feb 2005 Posts: 298 Location: ITALY

thanks! of people like you need this forum ...

I will make tests and update you.

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

Well done EDC. It is a good starting point.

I have done some commercial CCTALK apps. It is used in vending machines used on events.

One thing i like to warn for in general when i see serial reception code.
Thus not about your code but what i see in support : code that assumes that there will come data.
It is best never to assume that further data will arrive. There are different ways to deal with that.

first you can first count how much data is received. that way you know if you can read/process all data.
Another way is to use a simple state machine where you advance through states .
first you wait for data, when you have data you go to a next state. it is also important to consider timing. if for some time no data arrives you can reset your state.
because when you activate your code, you need to know what the data is. that what you think is the first byte is actually the first byte and not some data in the middle. of course you can check this with crc.
And you can use a WD timeout which is a rather cruel way.

EDC · Joined: 26 Mar 2014 Posts: 971

In my aplications I set Timeout if I receive first byte, then renev it every next one.
If message is complite I set Timeout = 0 and parse but if message is for example without end mark for too long then I clear state machine, reset index or force to parse. It depend of application.

Yeah. This is important notice. I was affected by that VB.Net code above Very Happy

[EDIT] Should be better Wink

atmega64 · Joined: 23 Feb 2005 Posts: 298 Location: ITALY

I obtained the BASCOM code from the VB.net code, which I had written ... and it works (obviously the timeout has to be managed etc ..)

a question ... there is a way in BASCOM to convert these commands to arrays ?

ReDim Preserve RxData (LenRx)
ReDim RxData (0)

CCTALK protocol reception code:

EDC · Joined: 26 Mar 2014 Posts: 971

I think that VB.Net code was not yours if you dont understand how ReDim works Very Happy

Read this for a moment https://www.dotnetperls.com/redim-vbnet

..then read this short explanation what Preserve means LINK

Above means that simple ReDim will resize Array but also zeroes it (fill it with zeros) while ReDim Preserve will leave original content and resize array (in your case create another next memory cell).

So in PC that Array can grow dinamically. In uC like AVR you must declare/guarantee array with some reasonably length, then operate on the index.

So code should look like this, I think: