试试这个看：

MScomm1发送：
Dim objMScomm
Set objMScomm=ScreenItems("MSComm1")
MSComm1.CommPort = 1
MSComm1.Settings = "9600,N,8,1"
MSComm1.InputLen = 1
MSComm1.PortOpen = True
objMScomm.Output="aaa"
MSComm1.PortOpen = False

MScomm1接收：
Dim objMScomm,data
Set objMScomm=ScreenItems("MSComm1")
MSComm1.CommPort = 1
MSComm1.Settings = "9600,N,8,1"
MSComm1.InputLen = 1024
MSComm1.PortOpen = True
objMScomm.InputLen=1
data=objMScomm.Input
HMIRuntime.Tags("char2").Write data
MSComm1.PortOpen = False

MSComm1为MSComm控件的名称！