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Side-Effects

Debugging programs with ISD51 has some side-effects.

  • Hardware breakpoints and Flash breakpoints always work-even when the interrupt system is disabled.
  • Software breakpoints and singled-stepping (even with hardware and flash breakpoints) work only when the ISD51 interrupt and the global interrupt system are enabled. You may, of course, disable ISD51 operation during critical program sections.
  • There are cases where the 8051 MCU blocks interrupts for more than one instruction cycle. This happens when your program accesses an interrupt enable register or an interrupt priority register. Also execution of the instruction RETI blocks interrupts for one additional instruction. In such situations, ISD51 steps over two or more assembler instructions when single-stepping.
  • ISD51 allows breakpoints even in ROM. If software breakpoints are set, the 8051 program runs under control of the ISD51 interrupt function and execution speed is degraded about 100x (programs run 100 times slower).
  • Breakpoints and single-stepping are not possible in 8051 interrupt functions that have the same or higher interrupt priority level than the ISD51 interrupt.
  • If the ISD51 interrupt is enabled, it is possible to stop the 8051 program execution from within the µVision Debugger using the Stop toolbar button.
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