Dear Jejomar,

thank you very much for your ongoing support !


After reading Bruce's latest advice, I modified 
the small demo program accordingly and could 
reproduce his modifications and results.

a) green led around critical ADC10 sequence ;  
b) TA1CCRO to 58 ;  ==>  interrupts 345x faster 
c) experiment with _bic versus _bis i.e. guard on/off
Result: the red LED is ON, the green LED is OFF (with guard);
    without guard  the green LED goes ON after some time (randomly)

Then, I added further modifications:

d) removed the 151ms-delay  ==> much higher ADC10 rate ;
e) changed %100 to %34483 w.r.t. "one second clock" ;

Results:  the red LED blinks with "one second" rate,
          the green LED "glows", 
          the program runs ok with the "guard" !

However, my concerns are not fully removed....
- The ADC10 has its own clock that is probably asynchronous 
  to the DSO  and is between 3.7 and 6.3 Mhz.
- With 13+16 = 29 ADC10-clocks we have a conversion time of 
  4.6 to 7.8 us !
- So, the critical window with CPUOFF ist 4.6 to 7.8 us wide.
- The Timer1 interrupts have a rate of  2 MHz / 58 = 35 kHz
- The Timer1 interrupt has a higher priority (29) than the 
  ADC10 interrupt (21).
Q Why is the critical window not hit by the higher interrupt ?


With thanks in advance & best regards, Uli