RDCU-02C

根据PC与FX系列PLC的传输应答过程，利用VB的MSComm控件可以编写如下通信程序实现PC与FX系列PLC之间的串行通信，以完成数据的读取。MSComm控件可以采用轮询或事件驱动的方法从端口获取数据。在这个例子中使用了轮询方法。

1）通信口初始化

Private Sub Initialize（）

MSComm1．CommPort =1

MSComm1．Settings = “9600,E,7,1”

MSComm1．InBufferSize = 1024

MSComml．OutBuffersize = 1024

MSComm1．InputLen = 0

MSComml．InputMode = comInputText

MSComm1．Handshaking = comNone

MSComm1．PortOpen = True

End Sub

2）请求通信与确认

Private Function MakeHandshaking（）As Boolean

Dim InPackage As String

MSComml．OutBufferCount = 0

MSComml．InBufferCount = 0

MSComml．OutPut = Chr（＆H5）

Do

DoEvents

Loop Until MSComml．InBufferCount = 1

InPackage = MSComml．Input

If InPackage = Chr（＆H6） Then

MakeHandShaking = True

Else

MakeHandshaking = False

End If

End Function

3）发送命令报文

Private Sub SendFrame ()

Dim Outstring As String

MSComml．OutBufferCount = 0

MSComml．InBufferCount = 0

Outstrin = Chr（＆H2）＋″on″＋″10F604″＋Chr（＆H3）＋″74″

MSComml．Output = Outstring

End Sub

4）读取应答报文

Private Sub ReceiveFrame（）

Dim Instring As String

Do

DoEvents

Loop Until MSComml．InBufferCount = 12

InString = MSComml．Inpult

End Sub