GameBoy\Opcode::opcode231 PHP Method

    public static function opcode231(Core $core)
    {
        $core->stackPointer = $core->unswtuw($core->stackPointer - 1);
        $core->memoryWrite($core->stackPointer, $core->programCounter >> 8);
        $core->stackPointer = $core->unswtuw($core->stackPointer - 1);
        $core->memoryWrite($core->stackPointer, $core->programCounter & 0xff);
        $core->programCounter = 0x20;
    }