msp430: external crystal test

crystal_test.c

// test external crystal by observing ACLK frequency on ACLK pin
// ACLK correspond to pin P1.0 in MSP430G2553 (see MSP430G2553 datasheet)
// an external crystal connects to the XIN, XOUT pins
// XIN and XOUT correspond to pins P2.6 and P2.7 respectively in MSP430G2553 (see MSP430G2553 datasheet)
// P1SEL = BIT0 and P1DIR = BIT0 show ACLK in P1.0 (see MSP430G2553 datasheet, pin functions)
// this only works with small crystals in cylindrical package

// stand-alone uC test:
// DVCC to 3.3V
// DVSS to GND
// RST' to 3.3V
// crystal between XIN and XOUT (as close as possible to the uC)
// oscilloscope probe to P1.0 and GND

#include <msp430g2553.h>
#define XT BIT0;                // BIT0 P1.0

void main(void){
  WDTCTL = WDTPW + WDTHOLD;     // stop watchdog timer
  BCSCTL3 = LFXT1S_0 + XCAP_3;  // external crystal, 12.5pF (this line of code generates the 32,768Hz square signal)
  P1SEL = XT;                   // port select: TA0.TACLK
  P1DIR = XT;                   // port select: ACLK on P1.0
  
  while(1);                     // do this forever
}