4.3 Instruction Description Example
The example description below is for the fictitious instruction,
FOO. The following example instruction was created to demonstrate how
the table fields (syntax, operands, operation, etc.) are used to describe the instructions
presented in Instruction Descriptions.
FOO
| FOO | The Header field summarizes what the instruction does | ||||||
|---|---|---|---|---|---|---|---|
| Syntax: | The Syntax field consists of an optional label, the instruction mnemonic, any optional extensions which exist for the instruction and the operands for the instruction. Most instructions support more than one operand variant to support the various addressing modes. In these circumstances, all possible instruction operands are listed beneath each other and are enclosed in braces. | ||||||
| Operands: | The Operands field describes the set of values that each of the operands may take. Operands may be accumulator registers, file registers, literal constants (signed or unsigned) or Working registers. | ||||||
| Operation: | The Operation field summarizes the operation performed by the instruction. | ||||||
| Status Affected: | The Status Affected field describes which bits of the STATUS Register are affected by the instruction. Status bits are listed by bit position in descending order. | ||||||
| Encoding: | The Encoding field shows how the instruction is bit encoded. Individual bit fields are explained in the Description field and complete encoding details are provided in Table 5.2. | ||||||
| Description: | The Description field describes in detail the operation performed by the instruction. A key for the encoding bits is also provided. | ||||||
| Words: | The Words field contains the number of program words that are used to store the instruction in memory. | ||||||
| Cycles: | The Cycles field contains the number of instruction cycles that are required to execute the instruction. | ||||||
| Examples: | The Examples field contains examples that demonstrate how the instruction operates. “Before” and “After” register snapshots are provided, which allow the user to clearly understand what operation the instruction performs. | ||||||