使用wincc flexible向串口发送字符串可以收到，发送16进制数据就不行。代码如下，是一个按钮点击以后触发的事件：
Dim scr
Dim com
Dim str
Dim senddata(5)
Set scr = HmiRuntime.Screens("SerialPort")
Set com = scr.ScreenItems("MSComm")

com.PortOpen = False

com.CommPort = 1
com.InBufferSize = 1024 '接收数据长度
com.OutBufferSize = 512 '发送数据长度
com.Settings = "9600,n,8,1"
com.InputMode = 0
com.PortOpen = True

senddata(0) = &H04
senddata(1) = &H30
senddata(2) = &H31
senddata(3) = &H4D
senddata(4) = &H31
senddata(5) = &H05
'com.Output = "0123456789" ‘发送字符串成功
com.Output= senddata ’发送16进制失败