根據PC與FX系列PLC的傳輸應答過程，利用VB的MSComm控件可以編寫如下通信程序實現PC與FX系列PLC之間的串行通信，以完成數據的讀取。MSComm控件可以采用輪詢或事件驅動的方法從端口獲取數據。在這個例子中使用了輪詢方法。

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）請求通信與確認

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）發送命令報文

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）讀取應答報文

Private Sub ReceiveFrame（）

Dim Instring As String

Do

DoEvents

Loop Until MSComml．InBufferCount = 12

InString = MSComml．Inpult

End Sub