English is currently available.
8051 Microcontrollers DISCUSSION
Code written for a classic 12-clock 8051 can produce unexpected timing on a newer compatible MCU. Which clock assumptions should be checked before reusing delay loops or timer reload values?
Is instruction-set compatibility enough to preserve the original timing?
No. Instruction compatibility does not guarantee the same number of oscillator clocks per instruction or the same timer clock. Check the selected system clock, divider and timer source in the exact device manual. EFM8 timer sources can be configurable, so applying a blanket divide-by-12 assumption can be wrong.
Replace a timing-critical busy loop with a hardware timer where appropriate and calculate from the timer's actual input frequency. For a 1 MHz timer tick, a 1 ms interval is 1,000 counts, giving a nominal 16-bit overflow preload of 64,536. That example applies only when the configured timer clock is really 1 MHz.
Measure a diagnostic output after initialization and again under normal interrupt load. Compiler optimization can change a software delay loop, while interrupt execution adds further variation. Keep clock configuration and timing calculations together in the project notes so a later oscillator change does not silently invalidate them.
