ZeroOperand.m

function [IR,AM,registers,memory ] = ZeroOperand(registers,memory,IR )
% Executes the zero operand instruction
    % No addressing mode return
    AM=[-1,-1];
    % increment PC by 1
     registers(1)=registers(1)+1;
     switch IR
         case 242 % RETURN from a subroutine call. The return address is restored from the stack
             % PC <= *SP (value of the top of the stack location is stored in the program counter PC)
             registers(1)=memory(registers(2)+1);
             % inc rease stack pointer value (SP <= SP +1)
             registers(2)=registers(2)+1;
         case 244 % INITSP SP=(0b11111111)
             registers(2)=255; 
         case 254 % NOP No Operation
         case 255 % RETURN (Stop execution)
         otherwise
             % This shouldn't show if you are using the right instructions
             error('can not recognise this zero instruction pattern');
     end
end