MSP430: Custom calibration for DCO

While using the launchpad and Value line chips, I was a little Disappointed in lack of calibration data and no way to reliably change the default settings. So I started flashing the DCO calibrations data –> original post http://www.43oh.com/forum/viewtopic.php?f=10&t=239&hilit=calibration
Now the default 1 8 12 and 16 MHZ settings are fine but what if you wanted a bunch of chips to run on 3MHz or 500KHz. Are you will to try and figure out the RSEL and MOD and DCO bits and start randomly flipping testing settings? To me this sounds like a long and boring process and I don’t have the time to test and try and get 2MHz, or what if I need 10MHz , my scope doesn’t even come close to that 🙁 .

So I decided to modify the TI DCO flash calibration code from TIs examples, these changes allow me to set the default and the other calibration data to the settings I want.
The few changes I made are,

  • Added Xcap setting to BCSCTL3 to make internal cap 12.5pF
  • Added custom constant to replace 1MHz default(244), – new one is for 2MHz

no other changes made to the code.

custom_dco

 

Now there is a few things to remember, This code will re-write over TI calibrated constants if you have An F series (IE everything but value line G series) chips. Or it will Write the calibration to the G line chips – which are not calibrated when you get them except the 1MHz default.

SO USE THIS CODE AT YOUR OWN RISK!!

 



//******************************************************************************
// Custom DCO settings- based on TI code example
//
// MSP430F20xx Demo - DCO Calibration Constants Programmer
//
// NOTE: THIS CODE REPLACES THE TI FACTORY-PROGRAMMED DCO CALIBRATION
// CONSTANTS LOCATED IN INFOA WITH NEW VALUES. USE ONLY IF THE ORIGINAL
// CONSTANTS ACCIDENTALLY GOT CORRUPTED OR ERASED.
//
//
// MSP430F20xx
// ---------------
// /|| XIN|-
// | | | 32kHz
// --|RST XOUT|-
// | |
// | P1.0|--> LED
// | P1.4|--> SMLCK = target DCO
// Orignal Code By
// A. Dannenberg
// Texas Instruments Inc.
// May 2007
// Built with CCE Version: 3.2.0 and IAR Embedded Workbench Version: 3.42A
//******************************************************************************
//******************************************************************************
/*Flash Custom DCO settings, This will replace The default 1MHz */
/* to use
//Custom calibration
BCSCTL1 = CALBC1_1MHZ; // Set range
DCOCTL = CALDCO_1MHZ; // Set DCO step + modulation
*/
//ACLK = LFXT1/8 = 32768/8, MCLK = SMCLK = target DCO
//* External watch crystal installed on XIN XOUT is required for ACLK *//
//******************************************************************************
#include "msp430f2013.h"
#define DELTA_CUSTOM 489 // 489 x 4096Hz = 2002944Hz or 2.02MHz
#define DELTA_8MHZ 1953 // 1953 x 4096Hz = 7.99MHz
#define DELTA_12MHZ 2930 // 2930 x 4096Hz = 12.00MHz
#define DELTA_16MHZ 3906 // 3906 x 4096Hz = 15.99MHz
unsigned char CAL_DATA[8]; // Temp. storage for constants
volatile unsigned int i;
int j;
char *Flash_ptrA; // Segment A pointer
void Set_DCO(unsigned int Delta);
void main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
for (i = 0; i < 0xfffe; i++); // Delay for XTAL stabilization P1OUT = 0x00; // Clear P1 output latches P1SEL = 0x10; // P1.4 SMCLK output P1DIR = 0x11; // P1.0,4 output BCSCTL3 = XCAP_3; // Set internal cap to 12.5 j = 0; // Reset pointer Set_DCO(DELTA_16MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Set_DCO(DELTA_12MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Set_DCO(DELTA_8MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Set_DCO(DELTA_CUSTOM); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Flash_ptrA = (char *)0x10C0; // Point to beginning of seg A FCTL2 = FWKEY + FSSEL0 + FN1; // MCLK/3 for Flash Timing Generator FCTL1 = FWKEY + ERASE; // Set Erase bit FCTL3 = FWKEY + LOCKA; // Clear LOCK & LOCKA bits *Flash_ptrA = 0x00; // Dummy write to erase Flash seg A FCTL1 = FWKEY + WRT; // Set WRT bit for write operation Flash_ptrA = (char *)0x10F8; // Point to beginning of cal consts for (j = 0; j < 8; j++) *Flash_ptrA++ = CAL_DATA[j]; // re-flash DCO calibration data FCTL1 = FWKEY; // Clear WRT bit FCTL3 = FWKEY + LOCKA + LOCK; // Set LOCK & LOCKA bit while (1) { P1OUT ^= 0x01; // Toggle LED for (i = 0; i < 0x4000; i++); // SW Delay } } void Set_DCO(unsigned int Delta) // Set DCO to selected frequency { unsigned int Compare, Oldcapture = 0; BCSCTL1 |= DIVA_3; // ACLK = LFXT1CLK/8 TACCTL0 = CM_1 + CCIS_1 + CAP; // CAP, ACLK TACTL = TASSEL_2 + MC_2 + TACLR; // SMCLK, cont-mode, clear while (1) { while (!(CCIFG & TACCTL0)); // Wait until capture occured TACCTL0 &= ~CCIFG; // Capture occured, clear flag Compare = TACCR0; // Get current captured SMCLK Compare = Compare - Oldcapture; // SMCLK difference Oldcapture = TACCR0; // Save current captured SMCLK if (Delta == Compare) break; // If equal, leave "while(1)" else if (Delta < Compare) { DCOCTL--; // DCO is too fast, slow it down if (DCOCTL == 0xFF) // Did DCO roll under? if (BCSCTL1 & 0x0f) BCSCTL1--; // Select lower RSEL } else { DCOCTL++; // DCO is too slow, speed it up if (DCOCTL == 0x00) // Did DCO roll over? if ((BCSCTL1 & 0x0f) != 0x0f) BCSCTL1++; // Sel higher RSEL } } TACCTL0 = 0; // Stop TACCR0 TACTL = 0; // Stop Timer_A BCSCTL1 &= ~DIVA_3; // ACLK = LFXT1CLK }

So you want a your own custom frequency, now the easiest way to do this is take your target clk speed and divide it by 4096. which 4096 is 32KHz clock divided by 8. For my 2MHz calculation I did 489 x 4096Hz = 2002944Hz or 2.02MHz
you division will get you close to the number you will need, round up or down according to your frequency. I choose to go a little over/ round up.

Remember the Faster your clock, the farther you will be away from your target
example - 488 x 4096 = 1,998,848
489 x 4096 = 2,002,944
difference 4,096

Its not too bad but if you are going for a specific CLK speed you may need to try a different method like an oscilloscope, and manually changing the DCO, RSEL, MOD bits .

FYI there is a test program included in the zip file to test your new calibration data.