Editing Intel 8085 (section)

====8-bit instructions====
All two-operand 8-bit arithmetic and logical (ALU) operations work on the 8-bit [[Accumulator (computing)|accumulator]] (the A register). For two-operand 8-bit operations, the other operand can be either an immediate value, another 8-bit register, or a memory cell addressed by the 16-bit register pair HL. The only 8-bit ALU operations that can have a destination other than the accumulator are the unary incrementation or decrementation instructions, which can operate on any 8-bit register or on memory addressed by HL, as for two-operand 8-bit operations. Direct copying is supported between any two 8-bit registers and between any 8-bit register and an HL-addressed memory cell, using the MOV instruction. An immediate value can also be moved into any of the foregoing destinations, using the MVI instruction. Due to the regular encoding of the MOV instruction (using nearly a quarter of the entire opcode space) there are redundant codes to copy a register into itself (''MOV B,B'', for instance), which are of little use, except for delays.<ref group="nb">Even so, there is no need for seven different effectively identical delay instructions, and they are also identical in effect and form to the NOP instruction, except that NOP conveniently has the opcode 00 hex.</ref> However, what would have been a copy from the HL-addressed cell into itself (i.e., ''MOV M,M'') instead encodes the [[HLT (x86 instruction)|HLT]] instruction, halting execution until an external reset or unmasked interrupt occurs.<ref group="nb">(The TRAP interrupt, being an [[Non-maskable interrupt|NMI]], can always bring the 8085 out of the HALT state.)</ref> <!-- It would be better if HLT were only mentioned here as regards opcode assignment and was explained operationally in a separate section about machine-control instructions-->