Simple-CPU

16-bit Instruction Word (IW) of ProjectCPU: (see as raw)

         			IW
	|----------------------------------

bit position |15 13| 12 0| |---------------------------------- field name | opcode | A | |---------------------------------- bit width | 3b | 13b | |----------------------------------

(Every memory location and W are 16 bits)

Instruction Set of ProjectCPU:

ADD -> unsigned Add opcode = 0 W = *A + W write(readFromAddress(A) +W) to W *A = value (content of) address A = mem[A] (mem means memory) = means write (assign)

NAND -> bitwise NAND opcode = 1 W = ~((*A) & W)

SRL -> Shift Right or Left opcode = 2 W = ((*A) <= 16) ? (W >> (*A)) : (W << ((*A) - 16))

LT -> Less Than opcode = 3 W = W < (*A)

BZ -> Branch on Zero opcode = 4 PC = (W == 0) ? *A : (PC+1)

CP2W -> Copy to W opcode = 5 W = *A

CPfW -> Copy from W opcode = 6 *A = W

MUL -> unsigned Multiply opcode = 7 W = lower16bit(W * (*A))

INDIRECT ADRESSING

There are no special instructions for indirect addressing. Instead, every instruction can operate in indirect addressing mode.

That is, if A==0, replace *A above with **4.

Every program starts like this:

0: CP2W 2 1: BZ 3 2: 0 3: 5 4: // indirection register 5: // program actually starts here