写入ByteArray和读出的数据不一致，很奇异,该怎么解决

                        var buffer:ByteArray=new ByteArray();

            buffer.writeByte(-48);
            
            var msg:String="";
            
            for(var i:int=0;i<buffer.length;i++){
                msg=msg+buffer[i]+",";
            }

            
            ExternalInterface.call("alert","connected："+msg);