MSP430F4152 setting baud rate

Hi Fran, 

with this much BR0 variance, I would look at the clock sourcing the peripheral first.  Presuming that the dco is sourcing mclk, take aclk and mclk out to their IO pins (pin tables begin on page 8 Of the DS) to be scoped.   Do this for multiple devices and after the dco has been configured for the 4mhz output.

let us know what you find.

OK, it will take me a day or two to get there.  It's all asses and alligators here at the moment.

I'll post what I find.

In addition to what Michael suggested, it would be helpful to see the code you are using for configuring the UCS clock module. You may not be setting the DCO/FLL registers properly.

Here's all I'm doing to init the clock.

int __low_level_init(void)
{
  volatile unsigned int i;                  // Use volatile to prevent removal by compiler optimization

  WDTCTL = WDTPW + WDTHOLD; // disable the watchdog
  // Setup the Clocks and Xtal
  FLL_CTL0 |= XCAP11PF;                     // Configure xtal load caps
  for (i = 0; i < 10000; i++);              // Delay for 32 kHz crystal to stabilize
 
  // Loop until Xtal fault is clear
  do
  {
    IFG1 &= ~OFIFG;                         // Clear osc fault flag
    for (i = 0; i < 1000; i++);             // Delay for osc to stabilize
  } while(IFG1 & OFIFG);                    // Check to see if osc flag is set
  

  SCFQCTL = SCFQ_4M;                        // DCO 4.183MHz
 
  
  return (1);                       // Initialize RAM locations.
}

It wasn't clear to me from the UM as to what else to do to the FLL registers, but that's probably my deficiency.

Also, I've made some quick measurements on ONE board.  ACLK is pretty good at 32771, but SMCLK is running at a stable 3.029 MHz, when set up for 4 MHz.  When I change it to SCFQ_2M, it's at 2.04 MHz.

Not sure what any of that means at the moment, just regurgitating what I see.

Wow!  What a difference.  I now have a solid 4.194 MHz.  I guess the default DCO range specification of 0.65 to 6.1 MHz was not good enough.

Hopefully, when I move this over to the other devices, my BR0 wobble disappears.

Thanks for the help!

Well, that looks like it's it.  I'm 3 for 3 in setting up the UART with the same parameters on 3 devices.

Thanks, again, for the help.

Fran

I guess the default DCO range specification of 0.65 to 6.1 MHz was not good enough. If you look at the datasheet, you’ll see that 0.65 to 6.1MHz is a typical value. However, best case it may go from 0.3 to 11.3MHz (if this can be called “best case“, as it means the individual frequencies are far apart) and worst case, It only spans 1.25 to 2.7MHz

Setting FN_2, the worst case (narrowest) range is from 2.5 to 6.5MHz.