HP18C & HP28C ROM checksum?


Does somebody know how are the ROM checksum correction WORDs or BYTEs in the HP18C and HP28C ROMs are calculated. I know how to verify them, but how they are calculated is a mystery to me. When using a correction WORD there are multiple solutions, when using a BYTE there's only one solution and none when the checksum without the last BYTE is #0000h.

So is there are a correction WORD or BYTE?

Where's the position in each block?

When it's a WORD, how they come to the used correction WORD?



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