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.