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assembly8051

Leading zeros in hex values

Reading over some assembly for a 8051 project and I'm having difficulty understanding why some hex values have leading zeros and some don't, am I right in presuming both examples set acc.5 to 1?

mov a, #020h

mov a, #20h

Solution

  • am I right in presuming both examples set acc.5 to 1?

    Yes.

    But your hidden question is: "Why have hex values a leading zero even if it seems not to be necessary?"

    Well, that's just for visual consistency with values beginning with 'A' to 'F'. If those would not start with a digit they would not be recognized as numbers but as identifiers.

        mov a, #0E0H  ; loads hex E0 (= dec 224) into ACC
    mov a, #E0H   ; loads the value of "E0H" into ACC, with any value defined as "E0H"

    The author likes to write all values the same way. If there's a value without zero it might be a typo, a missed case, from another author, or for any other reason.