Re: [avr-gcc-list] Small program for UART not working

[Anton Erasmus]

On 29 Aug 2005 at 17:24, Gary Bi wrote:

> Hi David and Ian,
> 
> Thanks for the help. I checked the fuses for mega101
> mode, it did set to ON. I uncheck it in AVR studio and
> program it, but this did not make improvement to the
> issue.
> 
> I shorted the PIN2 and PIN3 at the end of cable (the
> end plugs to PC RS232), I still can see the data was
> received through the loopback, demonstrated through
> LEDs on STK board. The RS232 cable is good, since I
> short the other end, I can see the chars typed
> displayed on the termial.
> 
> I'm suspecting the baud rate was not set accurately in
> Atmega128L, so cause the reception of PC side is not
> synchronized. For example, if I set to 115200, but not
> accurate, the number could be set as 115000, so I have
> some errors in PC terminal.
> 
> I tried to calculate the baud rate on scope, I found I
> can't get a exactly number, I can only get an
> estimate. Do you know if there's way to set the baud
> rate accurately?

Send 0xAA continiously. That way you get a nice
square wave at the baud rate frequency. If you drop
your baud rate to something like 9600, then you 
do not need such an accurate baud rate to get good results.
If it works at this low baud rate, but not at the higher baud rate,
then you know it is baud rate issues.

Regards
  Anton Erasmus


> Thanks,
> Gary
> 
> 
> 
> 
> --- David Brown <address@hidden> wrote:
> 
> > Hi,
> > 
> > Since you can see the data on your scope, and
> > loopback works fine when
> > shorting RX and TX pins, there seems to be nothing
> > wrong with the
> > microcontroller.  The things I would now check are
> > the baud rate (using the
> > scope), the RS-232 line drivers, the TX-RX
> > orientation (I've fixed many
> > communications problems by swapping the TX and RX
> > lines !), the cable
> > between the board and the PC (including the ground
> > line), and the PC serial
> > port.  It can be worth shorting the TX and RX pins
> > at the board end of the
> > cable and testing loop-back from the PC side using
> > TTP.
> > 
> > mvh.,
> > 
> > David
> > 
> > 
> > 
> > > Hi David,
> > >
> > > Thanks for the info. I downloaded Tera Term Pro
> > and
> > > installed it in my PC, it's a defenitely a better
> > > terminal simulation. Unfortunately I got the same
> > > result.
> > >
> > > My problem are:
> > >
> > > 1. Atmel128L has successfully sent out characters
> > in
> > > TX, but I can not receive it correctly in PC
> > termimal.
> > > When monitoring the TX pin in scope, I can see
> > char
> > > 'B' has been sent out continuouly.
> > > /* UART Transmit Complete Interrupt Function */
> > > SIGNAL(SIG_UART0_TRANS){
> > > outp('B',UDR0);
> > > }
> > > When I short TX and RX pin together in Atmel STK
> > > board, I can see the 'B' was displayed correctly
> > > (demonstrated using LEDs, PIN7-0 is for Bit7-0).
> > > /* UART Receive Complete Interrupt Function */
> > > SIGNAL(SIG_UART0_RECV){
> > > RxChar = inp(UDR0);
> > > outp(RxChar, PORTB);
> > > }
> > > What I receivd in TTP teminal is 0xA2 instead of
> > > character 'B' (0x42).
> > >
> > > 2. I did not set baud rate in the codes for Atmel,
> > in
> > > TTP, I will need to set the baud rate to 57600,
> > 8-N-1
> > > to get the RX working, so if I type 'C', I can see
> > the
> > > LEDs is demonstrated 'C' correctly. If the set the
> > > baud rate to 9600, 115200, etc. I can not get the
> > Rx
> > > working. This is very strange.
> > > So I have to comment out the two lines for baud:
> > >     //outp(0x0, UBRR0H);
> > >     //outp( (u08)UART_BAUD_SELECT, UBRR0L);
> > >
> > > The MCU is running at 7.3728Mhz, I set the baud
> > > parameter to 0x2F according to the datasheet.
> > > #define UART_BAUD_SELECT 0x2F //9600 baud
> > >
> > > There's typo in my previous email, what I want to
> > say
> > > is: I can see the character 'B' is sending out, I
> > just
> > > did not receive it correctly in PC.
> > >
> > > 3. Do you think it's possible it's related to a
> > defect
> > > MCU (ATMEGA128L)? I'm trying to buy a new
> > MCU(order
> > > ATMEGA128-16AI (16Mhz), but not sure if it will
> > work
> > > with 7.3728MHz crystal on STK or not.
> > >
> > > Thanks,
> > > Gary
> > >
> > >
> >
> ======================================================
> > > #include <avr/io.h>
> > > #include <avr/interrupt.h>
> > > #include <avr/signal.h>
> > > #include <avr/pgmspace.h>
> > >
> > > #define outp(a,b) b=a
> > > #define inp(a) a
> > > typedef unsigned char  u08;
> > > typedef unsigned short u16;
> > > #define UART_BAUD_SELECT 0x2F //9600 baud
> > >
> > > #define PRG_RDB( addr )   __LPM((unsigned
> > > short)(addr))
> > > #define BV(bit) (1 << (bit))
> > >
> > > /* UART global variables */
> > >
> > > volatile u08   RxChar;
> > > volatile int i = 0;
> > >
> > > /* UART Transmit Complete Interrupt Function */
> > > SIGNAL(SIG_UART0_TRANS)
> > > {
> > >  outp(0x43,UDR0);
> > > }
> > >
> > >
> > > /* UART Receive Complete Interrupt Function */
> > > SIGNAL(SIG_UART0_RECV)
> > > {
> > >     RxChar = inp(UDR0);
> > > outp(RxChar, PORTB);
> > > }
> > >
> > > void UART_Init(void)
> > > {
> > >     /* enable RxD/TxD and interrupts */
> > >
> > >
> > >
> >
> outp(BV(RXCIE0)|BV(TXCIE0)|BV(RXEN0)|BV(TXEN0),UCSR0B);
> > >     //outp(BV(RXCIE0)|BV(RXEN0)|BV(TXEN0),UCSR0B);
> > >
> > >     /* set baud rate */
> > >     //outp(0x0, UBRR0H);
> > >     //outp( (u08)UART_BAUD_SELECT, UBRR0L);
> > >
> > > // Async. mode, 8N1
> > >        UCSR0C =
> > >
> >
> (0<<UMSEL0)|(0<<UPM01)|(0<<UPM00)|(0<<USBS0)|(3<<UCSZ00)|(0<<UCPOL0);
> > >     /* enable interrupts */ > >     sei(); > > } > > > > int
> main(void) > > { > > outp(0xff, DDRB); //port B output > >
> UART_Init(); > > // for(;;){ > >     outp(0x41,UDR0); > > // } > >
> return 0; > > } > > > > > > > > > >
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-- 
A J Erasmus