请帮我分析下这个VB程序，下位机使用的是TEST程序，使用DEBUG372程序调试是成功的，但我自已做的上位机运行到CH375ReadData（）函数时返回值mLength为0，不知道哪儿出问题了？ If (Not IsOpen) Then IsOpen = mOpenDevice() If (Not IsOpen) Then Exit Sub End If End If statustxt.Text = "Running..." On Error Resume Next mTotal = Len(sendtxt.Text) If mTotal = 0 Then statustxt.Text = "Error：发送的内容为空！" MsgBox "发送的内容不能为空，请在发送区输入要发送的内容！", vbOKOnly + vbInformation, "提示信息!" Else For i = 0 To mTotal - 1 mBuffer.mBuff(i) = Mid(sendtxt.Text, i + 1, 1) Next i If (CH375Writedata(0, mBuffer, mTotal)) Then 　　　　 mLength = 5 If (CH375ReadData(0, mReadBuf, mLength)) Then If (mLength <> mTotal Or mLength = 0) Then mErrCnt = mErrCnt + 1 statustxt.Text = "error count:" & mErrCnt Else st = st & mReadBuf.mBuff(0) End If Else MsgBox "CH375读取数据错误", vbOKOnly + vbInformation, "提示信息！" End If Else MsgBox "CH375写数据错误", vbOKOnly + vbInformation, "提示信息！" End If If receiveflag = True Then receivetxt.Text = st Else End If End If Call Wait End Sub