Hi rlent
The below smartbear link might be of some help.
https://support.smartbear.com/testcomplete/docs/scripting/working-with/com-ports.html?q=Serial+port#_ga=1.151287417.1590760699.1470373334
Below is the sample VB Script code which is taken from the link
Sub Test
Dim Port, i, s
Set Port = dotNET.System_IO_Ports.SerialPort.zctor_4("COM1", 9600)
Port.Open
' Writing data to the port
Port.Write "A " & Chr(27)
' Waiting for response
aqUtils.Delay 1000
' Processing response
If Port.BytesToRead <> 0 Then
s = Port.ReadExisting
Log.Message s
Else
Log.Warning "No data"
End If
Port.Close
End Sub