Operand

Also called: operand address, memory operand

A value an instruction works on. In Tiny8 the instruction names the operand's memory address, and the CPU reads the value from there.

An operand is a value an instruction operates on. ADD needs two: the accumulator, and a second value from memory.

Instructions can supply operands in different ways:

From memory, by address. Tiny8's LOAD, ADD and SUB work this way: the address field holds an address, and the CPU reads the operand from that address.
Implicitly: the accumulator is always the other operand, so it needs no field.
Immediately, inside the instruction itself. Tiny8 has none, but the load immediate extension adds one.

The classic slip is to treat the address as the value. LOAD 9 doesn't put 9 in the ACC; it puts in whatever word is stored at address 9.

In Tiny8 the operand's journey is: address field → MAR (in D) → memory → MDR (in E1) → ALU or ACC (in E2).

Worked example

Example

Tiny8 executes 4C with ACC = 30. M[C] = 5.

Using the address as the value. The operand is the word stored at that address.
Forgetting the ACC is an operand too. Tiny8 instructions just don't need to name it.

Interactive questions with instant feedback and a worked solution for every wrong answer.

Operand is taught in Basic CPU / Computer Architecture.