Running code which has a repeating set of interrupt service routines for a timer and ADC. Program will execute for a minute or so and then freezes up or does not execute interrupts. Program toggles an output pin to show when interrupts are accessed. MCU clock frequency is 5.6MHz. I reduced the MAX JTAG Clock down to 50KHz based on the following Keil support doc. http://www.keil.com/support/docs/2935.htm Also tried the other options listed in the above support doc. System and hardware uVision3 V3.05 ULINK USB-JTAG jumper set to VCC/ext - correct. ADuC7020 Eval Board