Hi,
I don't have ready code samples, but I am pretty sure such communication is possible with the help of the CLR Bridge from TestComplete.
Try to search for C# / VB.Net code samples and port them to your scripting language (e.g. http://stackoverflow.com/questions/1243070/how-to-read-and-write-from-the-serial-port and http://stackoverflow.com/questions/13754694/what-is-the-correct-way-to-read-a-serial-port-using-net-framework).
Code from https://support.smartbear.com/viewarticle/9003/ section can be used as an example.
In the worst case you may create a regular .Net class library that implements port communication that you need (with the assistance from your developers?) and just call methods of this library from your TestComplete code via the mentioned CLR Bridge.