ALU

Opcodes

OpcodeActionFlagsDescription
ADD Rx,#

Rx <= Rx + Imm

Z, C

Rx is added to an Immediate 16 or 32 bit value with the result written back to Rx.

The C Flag is set on carry
(i.e. the register wraps from FFFFFFFF to 00000000).

The Z flag is set if the result is zero

SUB Rx,#

Rx <= Rx - Imm

Z, C

An immediate 16 or 32 bit value is subtracted from Rx and the result is written back to Rx.

The C Flag is set if there is a borrow (i.e. wraps from00000000 to FFFFFFFF).

The Z flag is set if the result is zero

CMP Rx,#

Z and C <= Rx = Imm

Z, C

An immediate 16 or 32 bit value is subtracted from Rx, but only flags are updated. Rx is unmodified.

The C Flag is set on borrow.

The Z flag is set if the result is zero

ADD Rx,Ry

Rx <= Rx + Ry

Z, C

Rx is added to Ry, and the result is written back into Rx.

The C Flag is set on carry.

The Z flag is set if the result is zero.

SUB Rx,Ry

Rx <= Rx - Ry

Z, C

Ry is subtracted from Rx, and the result is written back to Rx.

The C Flag is set on carry.

The Z flag is set if the result is zero.

CMP Rx,Ry

Z and C <= Rx = Ry

Z, C

Ry is subtracted from Rx, but only the flags are updated. Rx is unmodified.

The C Flag is set on borrow.

The Z flag is set if the result is zero.

MUL Rx,Ry

Rx ← Rx * Ry

Z

Rx and Ry are multiplied together, with the result put into Rx.

The Z flag is set if the result is zero.

DIV Rx,Ry

Rx ← Rx / Ry
Ry ← Rx % Ry

Z, C

This instruction performs two functions at once. Rx is divided by Ry, and the quotient is placed into Rx, and the remainder is placed into Ry.

The Z flag is set if the quotient (Rx) is zero.

The C flag is set if the remainder (Ry) is zero.

If dividing by 0 is attempted, will generate an error.

CLC

C ← 0

C

Clears the Carry Flag

SEC

C ← 1

C

Sets the Carry Flag

Notes

  • Z Flag used for result is zero
  • C Flag used for overflow on ALU