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 Posted: Apr 03, 2012 - 03:50 PM |
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Joined: Apr 03, 2012
Posts: 7
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Hi,
I'm starting my first project and I am trying to write a simple program to periodically output a character on a serial port. I've borrowed the code from tutorial programs I've seen and from the code in the app I need to modify.
If possible could someone eyeball and tell me what could b wrong? Obviously it is not doing what I expect.
Dev setup is:
Avr Studio 4.19
JTAGICE MKII
BDMicro-Mavric-IIB, ATmega128
Code:
int main()
{
cli();
//USART1
// communicates with PC at 57.6kpbs
// no interrupts, just polling
UCSR1A = 0;
UBRR1H = 0;
UBRR1L = 16; //assumes U2X set to 0
UCSR1B = 0x18; //0001 1000
UCSR1C = 0x06; //0000 0110
// sei();
char outChar = 'A';
_delay_ms(500);
while(1)
{
UDR1 = outChar;
_delay_ms(500);
}
}
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Posted: Apr 04, 2012 - 12:13 AM |
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Joined: Mar 28, 2001
Posts: 20374
Location: Sydney, Australia (Gum trees, Koalas and Kangaroos, No Edelweiss)
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First of all this is the Xmega forum, I'll move the thread.
2nd please use the CODE button when posting code. I'll fix this one.
Does the board have RS232 driver chips? I can't remember.
The data sheet has example code on how to PROPERLY send data out. |
_________________
John Samperi
Ampertronics Pty. Ltd.
www.ampertronics.com.au
* Electronic Design * Custom Products * Contract Assembly
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Posted: Apr 04, 2012 - 12:24 AM |
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Joined: Sep 04, 2002
Posts: 21261
Location: Orlando Florida
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| This should work, but only as long as the delay is longer than it takes the char to shift out. Usually you call a putchar(char c) function that polls the Uart Data Register Empty bit until it is empty, THEN you store the character in the UDR. Bet if you search for 'putchar' you'l see how someone else does it. |
_________________
Imagecraft compiler user
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Posted: Apr 04, 2012 - 12:48 AM |
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Joined: Nov 22, 2002
Posts: 12049
Location: Tangent, OR, USA
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Also, make sure that you are using a crystal to set the CPU clock frequency and that you have the baud rate bits set properly for the actual frequency of operation.
Jim |
_________________
Jim Wagner
Oregon Research Electronics, Consulting Div.
Tangent, OR, USA
"The only thing standing between us and victory is defeat" P.G.Wodhouse in Wooster & Jeeves series
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Posted: Apr 08, 2012 - 04:19 PM |
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Joined: Apr 05, 2010
Posts: 15
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I don't know how fast your clock source is, but the _delay_ms function has restrictions on how big the parameter value may be for correct operation:
The maximal possible delay is 262,14 ms / frequency in MHz.
Also you have to declare F_CPU before using the delay function. It should contain the CPU frequency in Hertz.
Both conditions can be found in the _delay_ms comments. Studio 5 shows it reliably on mouse over, maybe you should update your studio.
A better solution should be the active waiting approach, using a while loop (this is XMEGA code, check your datasheet for the status register contents of your controller):
Code:
// Wait for the transmit buffer to be empty
while ( !( USART_NAME.STATUS & USART_DREIF_bm) );
BTW: Makros like "USART_DREIF_bm" are defined in the header file for your cpu. The name of the file can be found in the file "io.h" in the WinAVR installation folder at avr/include/avr. For your ATmega128 it's the file "iom128.h" in the same directory. The makro names look similar to the register content names from the datasheet. Using the intelli sense in studio 5.1 it is easy to find them while typing - without leaving your own file. |
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Posted: Apr 18, 2012 - 03:28 AM |
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Joined: Apr 03, 2012
Posts: 7
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| Thanx for your help. Turned out I had some power issues. |
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