piccolo tmx320f28027 clock source changing issue

Non English-speaking writer here, beware! lol

My noob attempts correctly change clock source on a piccolo tmx320f28027 uP from a default
intern. OSC1 to an ext. 20MHZ osc. in a couple of random examples from DSP2802x_HeaderFiles
had failed, so help needed. thank you!

uP works excellent on IntOSC1 and an ext.osc. is running exactly 20 MHz
(no doubt, can see that with a tek scope).

My settings in DSP2802x_Examples.h:
#define DSP28_DIVSEL   2    // 120/2=60MHz
#define DSP28_PLLCR    6    // 20*6=120MHz
#define CPU_RATE   16.667L     // 60MHz CPU clock speed


Minor alteration in DSP2802x_SysCtrl.c external clock selection:
       //IntOsc1Sel();
       ExtClkSel ();
compilation... and.. uP stops in a very next func. call:
InitPll(DSP28_PLLCR,DSP28_DIVSEL);


void InitPll(Uint16 val, Uint16 divsel){
    ........
    if(SysCtrlRegs.PLLSTS.bit.MCLKSTS != 0){
    ........
    ........
          asm("        ESTOP0");   <--------------uP stops here
    }
}

I am reading "TMS320F2802x Piccolo System Control and Interrupts Reference Guide"   right now .
"Chapter 3 – Clocking" ....lost in info - no insight.