Program halts or operates incorrectly with ADuC842 at 16.78MHz. What might be
The ADuC842 can only operate at 16.78MHz when the supply voltage is 5V. Maximum
frequency is limited to 8.38MHz at 3V operation.
If the power supply decoupling, grounding of the printed circuit board design
is marginal, then increasing the clock rate may bring these problems to light,
causing the the program to stall more frequently.
=> with an analogue oscilloscope, scope the voltage on the Vdd and Ground lines
to assess how much noise is present and how it changes with frequency. If it is
more than a 100mV you have a problem.