Jeez Kai, you seem to have mastered it all, from astronomy, to mathemathics, to computers to electronics and embedded systems. Thank you very much for the information you provide. you are a great asset to the 8052 forum.

I just done google search and found some definitions:

EMC, or Electromagnetic Compatibility, is a measure of electrical equipment's ability to neither radiate nor conduct electromagnetic energy or be susceptible to outside energy sources within its normal operating environment.

EMI or electromagnetic interference, Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment. It can be induced intentionally, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like. [JP1] Synonym radio frequency interference RFI.

Mahmood