The Very Simple CPU simulator is an instructional aid for teaching microprocessor design. It allows the user to simulate the flow of data within this CPU as it fetches, decodes, and executes instructions. It uses animation to illustrate the flow of data between components, and highlights asserted control signals within the CPU. The user can simulate this CPU with a hard-wired control unit or a microcoded control unit.

The Very Simple CPU can access 64 bytes of memory, each byte being 8 bits wide. The CPU does this by outputting a 6-bit address on its output pins A[5..0] and reading in the 8-bit value from memory on its inputs D[7..0]. This CPU has only one programmer-accessible register, an 8-bit accumulator labeled AC. It has only four instructions in its instruction set, as shown below.

Instruction

Instruction Code

Operation

ADD

00AAAAAA

AC AC + M[AAAAAA]

AND

01AAAAAA

AC AC ^ M[AAAAAA]

JMP

10AAAAAA

Goto AAAAAA

INC

11XXXXXX

AC AC + 1


Chapters 6 and 7 of Computer Systems Organization and Architecture show how this CPU was designed in detail.

Click here for a video tour of the simulator (requires the Macromedia Shockwave Player, available at www.macromedia.com).

Screenshots:

Main Interface:

The view of the Register Section: