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--  作者：wangxinxin
--  发布时间：2010-12-14 14:36:19
--  开发语言中的VB串口通讯实例
高精度电压表(24bit) VB源程序
Dim PortValue As Integer `端口号选择1-4
Dim value As Double `当前一次取值
Dim value2 As Double `要显示的值
Dim valueSum As Double `和
Dim numCount As Double `算平均值是的计数个数
Dim func As Integer `功能号标志1-4
Dim valueFlag As Integer
Private Sub Check1_Click()
`自动刷新被选中则刷新按钮无效
If Check1.value Then
Command1.Enabled = False
Else
Command1.Enabled = True

Command1.SetFocus
End If
End Sub
Private Sub Command1_Click()
`显示
Call display
End Sub
Private Sub Command2_Click()
valueSum = 0 `清计数和
numCount = 1 `清计数个数
Label6.Caption = Str(numCount - 1) `显示复位
value = 0
value2 = 0
valueFlag = 0
Call display
End Sub
Private Sub Form_Activate()
numCount = 1
value = 0
valueSum = 0
PortValue = 1
Text1.Visible = False
Label6.Caption = 0
Option1(0).value = True
Option2(0).value = True
Command1.SetFocus
Label1.Caption = Format(value2 0.000000)
For i = 0 To 3
If Option2(i).value = True Then
func = i + 1
End If
Next i
Check1.value = 1
`Call ComPortOpen
End Sub
Public Sub ComPortOpen() `开串口
With MSComm1
.CommPort = PortValue `使用COM1
.Settings = 9600N81 `设置通信口参数
.InBufferSize = 40
`设置MSComm1接收缓冲区为40字节
`.OutBufferSize = 2
`设置MSComm1发送缓冲区为2字节
.InputMode = comInputModeBinary
`设置接收数据模式为二进制形式
.InputLen = 1
`设置Input 一次从接收缓冲读取字节数为1
`.SThreshold = 1
`设置Output 一次从发送缓冲读取字节数为1
.InBufferCount = 0 `清除接收缓冲区
`.OutBufferCount = 0 `清除发送缓冲区
`MaxW = -99
`最大值赋初值
`MinW = 99 `最小值赋初值
`w = 0
`数据个数计数器清零
.RThreshold = 1
On Error Resume Next
`设置接收一个字节产生OnComm事件
If .PortOpen = False Then
`判断通信口是否打开
.PortOpen = True `打开通信口
If Err Then `错误处理
msg = MsgBox( 串口 COM PortValue 无效！ vbOKOnly 警告)
Exit Sub
End If
End If
End With
`MsgBox 端口已打开
End Sub
Public Sub ComPortClose() `关串口
MSComm1.PortOpen = False
` MsgBox 端口已关闭
End Sub
Private Sub MSComm1_OnComm()
Call recive
End Sub
Private Sub Option1_Click(Index As Integer)
If MSComm1.PortOpen = True Then
Call ComPortClose
End If
PortValue = Index + 1
Call ComPortOpen
End Sub
Private Sub recive() `检测起始位并接收数据
Dim Buffer As Variant
Dim Arr() As Byte
Dim inData(5) As Byte
Dim count As Integer
Dim temp As Byte

` MsgBox OnComm
With MSComm1

Select Case .CommEvent
`判断MSComm1通信事件
Case comEvReceive
`收到Rthreshold个字节产生的接收事件
Buffer = .Input
Arr = Buffer

`读取一个接收字节
` Text1.Text = Arr(0)
If Arr(0) = H1B Then
.RThreshold = 0
Do
DoEvents
Loop Until .InBufferCount >= 4

For i = 1 To 4
`count = .InBufferCount
Buffer = .Input
Arr = Buffer
inData(i) = Arr(0)
Next i
If inData(4) = HA Then
If (inData(1) Mod 64) >= 32 Then
.RThreshold = 1
Exit Sub
End If
valueFlag = 1
`0.000003814697265625
temp = inData(1) Mod 16
If temp <= 7 Then
value = inData(1) Mod 8
value = value * 256 * 256
value = value + Val(inData(2)) * 256
value = value + Val(inData(3))
value = value * 3.814697265625E-06
`Text1.Text = Format(value 0.000000)
Else
value = inData(1) Mod 8
value = value * 256 * 256
value = value + Val(inData(2)) * 256
value = value + Val(inData(3))
value = value * 3.814697265625E-06
value = 0 - value
End If
temp = inData(1) Mod 128
` test OF
If temp >= 64 Then
If value < 0 Then
value = value - 0.000004
Else
value = value + 0.000004
End If
End If
`检测自动刷新
If Check1.value Then
`valueFlag = 1
Call display
End If