I have questions regarding some x86 instructions that were documented for the 80386 and later x86 CPUs, but not for earlier chips.
"OR reg/mem16, immed8" (0x83/1) "AND reg/mem16, immed8" (0x83/4) and "XOR reg/mem16, immed8" (0x83/6) These opcodes are "not used" on 8086/8088 according to this manual: https://edge.edx.org/c4x/BITSPilani/EEE231/asset/8086_family_Users_Manual_1_.pdf page 4-31 (but the meaning of "not used" is unclear). Old assemblers seem to avoid generating these, even if this means a four-byte instruction instead of a three-byte one (except for AX).
XLAT with a segment override prefix: Manuals for 8086 and 80286 only mention that it uses the DS register. It was first mentioned in the 80386 manual that it accepts segment prefixes.
Does somebody have any information on what these instructions actually do on CPUs where they are undocumented (8086/8088/80286/NEC V20)?
