Content deleted Content added
mv sw opcodes to bottom; cvt example cpu opcode table to subheading of CPUs |
→Sample opcode table: Combined paragraphs |
||
Line 12:
This table shows opcodes of a simple 8-bit microprocessor, the [[Intel 8008]] from 1972.
Each opcode is 8 [[bit]]s long. Each is shown as a [[Binary number|binary]] pattern of ones and zeros in the '''Opcode''' column. Up to two additional fields may be embedded into the opcode. Some 3-bit fields are labeled DDD, SSS, CC, and ALU. The SSS (source) and DDD (destination) fields specify one of the eight possible 8008 [[Processor register|registers]] or memory: A, B, C, D, E, H, L, or M. CC specifies a condition that will activate certain JMP, CAL, and RET instructions. ALU specifies one of a possible eight [[arithmetic logic unit]] functions to be performed during an instruction, specifically, add, add with carry, subtract, subtract with borrow, logical AND, logical XOR, logical OR, and compare. The '''X''' in some fields means that either a 1 or 0 can be inserted with [[Don't-care term|no effect]].
The fixed ones and zeros are combined with the parameter fields to build the 8-bit opcode. Additionally, the full instruction might require one or two additional bytes of operands. These are shown in the second major column of the table labeled '''Operands'''. If no operands are required, the column is filled with a dash (—).
Line 20 ⟶ 18:
Since the ones and zeros are difficult to remember, the '''Mnemonic''' column shows a short, easy to remember letter code that an [[assembly language]] programmer may use to invoke the required opcode.
The '''Description''' column shows the
{|class="wikitable" style="text-align:center"
| |||