vb mscomm 接收不到数据,该如何解决

vb mscomm 接收不到数据

Private Sub Form_Load()
Dim i As Integer
If MSComm1.PortOpen = True Then
MSComm1.PortOpen = False
End If '先判断串口是否关闭，如果打开则关闭
MSComm1.CommPort = 5 'COM端口
MSComm1.Settings = "115200,n,8,1"
MSComm1.InputLen = 0 '读取接收缓冲区的所有字符
MSComm1.InputMode = comInputModeBinary '采用二进制传输
MSComm1.InBufferSize = 1024 '接受缓冲区为1024字节
MSComm1.OutBufferSize = 2048 '发送缓冲区位2048字节
MSComm1.InBufferCount = 0 '清空接受缓冲区
MSComm1.OutBufferCount = 0 '清空传输缓冲区
MSComm1.SThreshold = 0 '禁止发送事件
MSComm1.RThreshold = 1 '产生MSComm事件
Command2.Enabled = False '初始化时设置“关闭”按钮不可用
End Sub

Private Sub MSComm1_OnComm()

Dim inbyte() As Byte '存储接收串口数据
Dim buffer As String '存储处理后的串口数据
Dim lenbuffer As Integer '存储处理后的串口数据长度
Dim i As Integer '设置循环变量

Select Case MSComm1.CommEvent
Case comEvReceive
inbyte = MSComm1.Input
For i = LBound(inbyte) To UBound(inbyte)

If Len(Hex(inbyte(i))) = 1 Then
buffer = buffer + "0" + Hex(inbyte(i)) + Chr(32)

Else
buffer = buffer + Hex(inbyte(i)) + Chr(32)
End If

lenbuffer = Len(Replace(Trim(buffer), " ", ""))

Select Case lenbuffer
Case Is = 14
If CByte("&H" & (Mid(Replace(buffer, " ", ""), 1, 2))) = &HAA _
And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 4 + 1, 2)) = &H42 _
And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 2 + 1, 2)) = &H42 Then
If "&H" & (Mid(Replace(buffer, " ", ""), 14 - 12 + 1, 2)) = &H55 Then

If "&H" & (Mid(Replace(buffer, " ", ""), 14 - 10 + 1, 2)) = &H43 _
And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 8 + 1, 2)) = &H47 _
And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 6 + 1, 2)) = &H8A Then

Text2.Text = "测试通过"
End If

End If
End If

case is = 18
....... 省略

End Select
Next i
End Sub

想问下，为什么上位机接收不到数据？？？ VB mscomm 数据接收
[解决办法]
OnComm事件代码
缺End Select
Next i位置错误

按我在2楼的接收代码，是能接收到数据的。
请降低波特率调试代码，或许USB转RS232线质量有问题导致。
[解决办法]
把收到的数据全部输出来显示,再与发送的数据相比较,看看到底是完全不对,还是顺序不对,还是有缺失,再进行下一步排查.
[解决办法]
应该是上位机代码屏蔽掉了一些数据。

如果你要调试接收是否正常，把你那些判断条件什么的都注释掉，把接收到的所有数据都显示出来。

[解决办法]
将buffer定义为窗体变量

Option Explicit
    Dim buffer As String
    
Private Sub Form_Load()
    Dim i As Integer
    If MSComm1.PortOpen = True Then 
 
        MSComm1.PortOpen = False
    End If
    MSComm1.CommPort = 1
    MSComm1.Settings = "115200,n,8,1"
    MSComm1.InputLen = 0
    MSComm1.InputMode = comInputModeBinary
    MSComm1.InBufferSize = 1024
    MSComm1.OutBufferSize = 2048
    MSComm1.InBufferCount = 0
    MSComm1.OutBufferCount = 0
    MSComm1.SThreshold = 0
    MSComm1.RThreshold = 1
    MSComm1.PortOpen = True '打开COM口
    Command2.Enabled = False
End Sub
 
Private Sub MSComm1_OnComm()
    Dim inbyte() As Byte
    Dim lenbuffer As Integer
    Dim i As Integer
    Select Case MSComm1.CommEvent
        Case comEvReceive
            inbyte = MSComm1.Input
            For i = LBound(inbyte) To UBound(inbyte)
                If Len(Hex(inbyte(i))) = 1 Then
                    buffer = buffer + "0" + Hex(inbyte(i)) + Chr(32)
                Else
                    buffer = buffer + Hex(inbyte(i)) + Chr(32)
                End If
            Next i
            Text1 = buffer
            lenbuffer = Len(Replace(Trim(buffer), " ", ""))
            Select Case lenbuffer
                Case Is = 14
                    If CByte("&H" & (Mid(Replace(buffer, " ", ""), 1, 2))) = &HAA _ 
 
                       And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 4 + 1, 2)) = &H42 _
                       And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 2 + 1, 2)) = &H42 Then
                           If "&H" & (Mid(Replace(buffer, " ", ""), 14 - 12 + 1, 2)) = &H55 Then
                               If "&H" & (Mid(Replace(buffer, " ", ""), 14 - 10 + 1, 2)) = &H43 _
                                    And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 8 + 1, 2)) = &H47 _
                                    And "&H" & (Mid(Replace(buffer, " ", ""), 14 - 6 + 1, 2)) = &H8A Then
                                    Text2.Text = "????"
                               End If
                           End If
                    End If
             End Select
    End Select
End Sub

[解决办法]

接收数据是固定字节长度的话，由于可以设置MSComm1.RThreshold为固定字节长度，buffer定义于为过程变量，接收代码照你原先的是没问题的。
而接收不定长的字节，只能设置MSComm1.RThreshold = 1，而COM口硬件原因，大于8字节以上的数据到达COM口会多次触发OnComm事件，buffer定义于为过程变量会导致接收字节不完整有丢数据现象，所以buffer定义于为全局变量。
[解决办法]
我一般的做法是,收到数据先检查长度,再与已存储的长度相加,看看是不是已经达到我要求的长度.

如果达到或超过,就进入处理流程.

处理流程里会找到有效数据的头与尾,并清空尾部数据以前的数据,保证未处理的数据是在缓冲区开头.

如此周而复始.
[解决办法]
推荐使用portmon软件辅助串口通讯调试。

vb mscomm 接收不到数据,该如何解决

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