uart receive problems

[robmitch]

contacted manufacturer. default baud9600, one stop bit, no parity... which is what i was using. Will try and look with scope, but might take a while to get one to use...

 

[ericgibbs]

contacted manufacturer. default baud9600, one stop bit, no parity... which is what i was using. Will try and look with scope, but might take a while to get one to use...

hi Rob,

If you connect a MAX232 to the Compass output you will be able to use a PC to communicate with the Compass.

 

[Mr RB]

I have conneced it all up, although when I read rx data, I only get, 00, as well as a framing error and overrun error, after a couple of reads. Also, that was after a lot of coaxing to get it to actually read uart1 instead of the default uart0...

It seems as though there is always one char available at startup (after entering main() ), even with the module unpowered (value also 00). Then, when I power the module, more become available (all 00, as mentioned). I tried in interrupt mode and polling mode.
...

That is a pretty common problem, getting a 0x00 on startup with a framing error, it means something is holding that pin low at startup.

Try putting a delay in your startup code where you set the pin directions, then the delay (this lets the pin voltages settle etc), THEN initialise the UART.

I'm not sure why you get the same problem "after a couple of reads" but I would definitely look at the problem happening at startup first, that might lead to solving the second problem.

 

[robmitch]

It's alive! My first microcontroller interface!

Thanks guys. I ended up relaying everything from compass on UART1 to hyperterminal via UART0 and its max232. Wasnt getting any readings, and checked connections again... I think they have mis-labelled the rx/tx pins on the compass module, because it works now having swapped the lines - so now they are not crossed-over (rx-rx and tx-tx). Then again, I have been known to get things wrong when it comes to connecting things on the opposite side of a board to the drawing, when a 50/50 chance will get it wrong...

Some output:
Next Reading
$H,109*3A
Next Reading
$H,110*32
Next Reading
$H,110*32
Next Reading
$H,106*35

(Mike, my getChar() routine sent the received char to the hyperterminal, so thats why the $ appears in above readings)

The 109, 110, and 106 are heading degrees

Wow, this site and you guys are awesome. Standby for more problems from me.
Cheers,
Rob

 

[engiah]

i have a problem whith the boudrate when i am using the soft uart of pic mcu
plz i need a help

 

[robmitch]

engiah,
I am pretty new myself. I havent used a software uart. Maybe someone else here can help you out.
Cheers,
Rob

 

[Mr RB]

I have a couple of projects on my page that use a soft uart on PIC.

This one uses PIC 16F876 in assembler and sends 31250 baud for MIDI;
(it says C but the uart "send byte" code is in assembler)
MIDI-Bash2 MIDI drum controller

This page has 4 projects in C. Project3 sends and receives software uart;
Connect JuneBug to serial port and Sharp GP2 sensor

 

[engiah]

THX 4 u rob
and THX 4 u MR RB

 

[skidd10]

sir robmitch,
can u post ur code on receiving data from the compass?, im also dealing with the same problem about the electronic compass. can i become ur apprentice?!!

 

[robmitch]

skidd10,
are you using the same compass module?

 

[skidd10]

ahm,nope,but we are using the same specs of electronic compass ..



here is the link

https://www.electro-tech-online.com/custompdfs/2009/10/Electronic20Compass.pdf

 

[skidd10]

sir rob,
.at least i can base my code with yours.please share your knowledge my mentor.
thanks!

 

[robmitch]

Skidd10,
Sorry for the delay. Here is some code (not very good) that I use to get the compass heading from the byte stream


unsigned char cReceived=0;

// Then, whilst in the main loop, poll for uart receive
if(U1STAT0 & 0x80) // There is receive data available
{
cCompassByte = U1RXD;// Get received byte
CompassReceive(cCompassByte); // Do something with character received
}

// Here, I want to
//=======================================================
void CompassReceive(unsigned char ch)
//=======================================================
{
// Look for $ - frame started
if(ch==0x24)
{
cReceived = 1;
c1=ch;
cReceived++;
return;
}

if(ch)
{
if(cReceived==2)
c2 = ch;
else if(cReceived==3)
c3 = ch;
else if(cReceived==4) // This will be hundreds
cHeading[0] = ch;
else if(cReceived==5) // This will be tens
cHeading[1] = ch;
else if(cReceived==6) // This will be the units
{
cHeading[2] = ch;
nHeading = atoi(&cHeading[0]); //convert to integer
}
else if(cReceived==7)
c7 = ch;
else if(cReceived==8)
c8 = ch;
else if(cReceived==9)
c9 = ch;
else if(cReceived==10)
c10 = ch;
else if(cReceived==11)
{
c11 = ch;
cReceived = 0;
return;
}
else {}

cReceived++;
}
}

 

[skidd10]

ahm,sir rob,
i think u havent included the initiallization?can you share sir the whole code.
thanks for the sample code!

 

[skidd10]

sir rob,how do you connect the compass to uart0 to uart1?

 

[skidd10]

if(ch) ======>>>>>sir rob,what is our condition here?
{
if(cReceived==2)
c2 = ch;
else if(cReceived==3)
c3 = ch;
else if(cReceived==4) // This will be hundreds
cHeading[0] = ch;
else if(cReceived==5) // This will be tens
cHeading[1] = ch;
else if(cReceived==6) // This will be the units

 

[robmitch]

skidd10,
You will have to look up your mcu manual for setting up/initiallising uart with whatever baud rate etc that your compass module has. Other than that, simple wire the compass tx/rx pins to the mcu tx/rx pins, but not necessarily in that order.

if(ch) tests if ch != 0x00 (I put this in since the uart initially sends a 0x00 on startup)

You will be able to make the code much better than this - I was just trying to spell things out.
Cheers,
Rob