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Does setting the NOP instructions to unused areas of the ROM valid?

Latest Updated:03/01/2005

Question:

(CPU)  As a countermeasure against program malfunction, is the following measure valid ?
Setting the NOP instructions to unused areas of the ROM/RAM and,
setting a jump instruction at the end of each unused area for jumping to the start address of the program at reset. [2005/03/01]

Answer:

Yes, this should work for a malfunction if the program counter specifies the unused area of the ROM/RAM.
A similar valid method is:
Set the BRK instruction (00h) to the entire unused area of the ROM/RAM and,
set the start address of the program at reset to the vector of the BRK instruction interrupt.
In both cases, since the malfunction causes internal state instability, remember to reset all SFR/RAM, including unused functions. (#104746)
Suitable Products
3803H
3803L
3823
3850A
3858
38D2
38D5
7544
7545
7546
7547
7548
7549