Need Help w/ MSP430 UART Tx

Hi,

I'm having trouble doing a simple character transmission on the
MSP430F149 UART.  I'm using SoftBaugh's ES149 eval board w/ICC430
compiler.  The board has a 32768 Hz clock. I've verifed that it runs
through the program.  When I probe at pin UTXD0 with an oscope, all I
see is a high signal.  Can anyone help?

Thanks,

Valerie


#include <msp430x14x.h>

void main() { 

      // avert Watchdog reset 
  WDTCTL = WDTPW + WDTHOLD; 

   //UART init
  BCSCTL1 = 0;                          // ACLK = LFXT1 = HF XTAL
  BCSCTL2 |= SELM1+SELM0;               // MCLK = LFXT1 (safe)
  UCTL0 = 0x11;                  	// 8-bit character, set SWRST
  UTCTL0 = SSEL0;                       // UCLK = ACLK
  UBR00 = 0x00;                         // 9600 baud ACLK = 32768 Hz
  UBR10 = 0x03;                         // Values from table
  UMCTL0 = 0x4A;                        // Modulation
  ME1 |= UTXE0 + URXE0;                 // Enable USART0 TXD/RXD
  P3SEL |= 0x30;                        // P3.4,5 = USART0 TXD/RXD
  P3DIR |= 0x10;                        // P3.4 output direction
  
// infinite transmit loop
  while(1)
 {
  while ((IFG1 & UTXIFG0) == 0);        // USART0 TX buffer ready?
  TXBUF0 = 0x59;                      // output 'V' on TXBUF0   
  }
  
}

vbark66@yahoo.com (V Barker) wrote in 
news:a5aff881.0403101653.7dd0d9ad@posting.google.com:
> I'm having trouble doing a simple character transmission on the
> MSP430F149 UART.  I'm using SoftBaugh's ES149 eval board w/ICC430
> compiler.  The board has a 32768 Hz clock. I've verifed that it runs
> through the program.  When I probe at pin UTXD0 with an oscope, all I
> see is a high signal.  Can anyone help?

high is good, thats idle.

> #include <msp430x14x.h>
> 
> void main() { 
> 
>       // avert Watchdog reset 
>   WDTCTL = WDTPW + WDTHOLD; 
> 
>    //UART init
>   BCSCTL1 = 0;                          // ACLK = LFXT1 = HF XTAL
>   BCSCTL2 |= SELM1+SELM0;               // MCLK = LFXT1 (safe)
>   UCTL0 = 0x11;                       // 8-bit character, set SWRST

why dont you use the bit names here too, makes it easier to read the 
code...

>   UTCTL0 = SSEL0;                       // UCLK = ACLK

you should not clear TXEPT here. when you write software that checks if the 
flag is set before writing a character, it will never work...

>   UBR00 = 0x00;                         // 9600 baud ACLK = 32768 Hz
>   UBR10 = 0x03;                         // Values from table
>   UMCTL0 = 0x4A;                        // Modulation

you wont be happy with these settings, you'll get up to 17% error for the 
bit times with is much larger than allowed. typicaly you should stay below 
2%

you can use this form to calcualte baudrate settings and errors:
http://mspgcc.sourceforge.net/baudrate.html

if you want to keep the watch crystal, then you need to implement the FLL 
and use a higher clock frequency on SMCLK to drive the UART.

>   ME1 |= UTXE0 + URXE0;                 // Enable USART0 TXD/RXD
>   P3SEL |= 0x30;                        // P3.4,5 = USART0 TXD/RXD
>   P3DIR |= 0x10;                        // P3.4 output direction

i usualy use the BIT* defines from the msp header files, like
P3SEL |= BIT4|BIT5;
that way you can make shorter comments ;-)

> // infinite transmit loop
>   while(1)
>  {
>   while ((IFG1 & UTXIFG0) == 0);        // USART0 TX buffer ready?
>   TXBUF0 = 0x59;                      // output 'V' on TXBUF0   

i usualy poll TXEPT in UTCTL0

>   }
>   
> }

chris

-- 
GCC for MSP430: http://mspgcc.sf.net
Chris <cliechti@gmx.net>

Chris,  

Your tips worked! I'm going to take your advice and install a HF clock
on the board for more accuracy.

Thanks for helping out an ME trying to be an embedded systems
programmer.

-Valerie 
Chris Liechti <cliechti@gmx.net> wrote in message news:<Xns94A917A5C5586cliechtigmxnet@62.2.16.4>...
> vbark66@yahoo.com (V Barker) wrote in 
> news:a5aff881.0403101653.7dd0d9ad@posting.google.com:
> > I'm having trouble doing a simple character transmission on the
> > MSP430F149 UART.  I'm using SoftBaugh's ES149 eval board w/ICC430
> > compiler.  The board has a 32768 Hz clock. I've verifed that it runs
> > through the program.  When I probe at pin UTXD0 with an oscope, all I
> > see is a high signal.  Can anyone help?
> 
> high is good, thats idle.
> 
> > #include <msp430x14x.h>
> > 
> > void main() { 
> > 
> >       // avert Watchdog reset 
> >   WDTCTL = WDTPW + WDTHOLD; 
> > 
> >    //UART init
> >   BCSCTL1 = 0;                          // ACLK = LFXT1 = HF XTAL
> >   BCSCTL2 |= SELM1+SELM0;               // MCLK = LFXT1 (safe)
> >   UCTL0 = 0x11;                       // 8-bit character, set SWRST
> 
> why dont you use the bit names here too, makes it easier to read the 
> code...
> 
> >   UTCTL0 = SSEL0;                       // UCLK = ACLK
> 
> you should not clear TXEPT here. when you write software that checks if the 
> flag is set before writing a character, it will never work...
> 
> >   UBR00 = 0x00;                         // 9600 baud ACLK = 32768 Hz
> >   UBR10 = 0x03;                         // Values from table
> >   UMCTL0 = 0x4A;                        // Modulation
> 
> you wont be happy with these settings, you'll get up to 17% error for the 
> bit times with is much larger than allowed. typicaly you should stay below 
> 2%
> 
> you can use this form to calcualte baudrate settings and errors:
> http://mspgcc.sourceforge.net/baudrate.html
> 
> if you want to keep the watch crystal, then you need to implement the FLL 
> and use a higher clock frequency on SMCLK to drive the UART.
> 
> >   ME1 |= UTXE0 + URXE0;                 // Enable USART0 TXD/RXD
> >   P3SEL |= 0x30;                        // P3.4,5 = USART0 TXD/RXD
> >   P3DIR |= 0x10;                        // P3.4 output direction
> 
> i usualy use the BIT* defines from the msp header files, like
> P3SEL |= BIT4|BIT5;
> that way you can make shorter comments ;-)
> 
> > // infinite transmit loop
> >   while(1)
> >  {
> >   while ((IFG1 & UTXIFG0) == 0);        // USART0 TX buffer ready?
> >   TXBUF0 = 0x59;                      // output 'V' on TXBUF0   
> 
> i usualy poll TXEPT in UTCTL0
> 
> >   }
>  
> > }
> 
> chris