5 ms·
Interesting discoveries. Perhaps some of the multi-port features on registers were for some of the REP features (ie: REP STOSB/MOVSB which updated multiple regi
by mmastrac 6y ago
Interesting discoveries. Perhaps some of the multi-port features on registers were for some of the REP features (ie: REP STOSB/MOVSB which updated multiple register) or some of the more generic instruction like PUSH/POP?
- EvanAnderson 6y agoThe plumbing around the BX/BH-BL registers is something I'd love to look at. BX, BP, SI, and DI were the only registers available for indexable operations (think "MOV WORD PTR [BX+2], AX"), and I wonder if the genesis of this behavior sits at the register file, or further away. BX/BH-BL is the only register capable of being used for indexable operations that is also 8-bit addressable.
- drmpeg 6y agoA byte addressable index register was required for 8080 assembly language compatibility to the H and L registers.
- EvanAnderson 6y agoBy "genesis of this behavior" I meant the implementation, not the reason (spec) for the behavior.