Each redcode instruction contains two operands. An operand is composed of an addressing mode and a number. The first operand is known as the A operand and the second as the B operand.

mov.i $1, #2

In the above example, the A operand is $1 and the B operand is #2.

The A addressing mode is $ (direct) and the A number is 1. The B addressing mode is # (immediate) and the B number is 2.

If no addressing mode is specified for an operand, the Parser inserts a default addressing mode of $ (direct).

Some opcodes only require a single operand in order to be successfully parsed. When this is the case, the parser inserts $0 as the second operand. In these situations the opcode determines whether the A or B operand is inserted.