I provide detailed information and working examples for doing Serial
I/O with Excel VBA.
In the Files Area folder: "VBA For the Serial Port".

The ReadMe should be consulted first.

One of the Workbooks [Serial IO Only Vers 082.xls] is a ready to
use, general purpose, serial I/O tool which does ASCII or
binary/Hex/BCD I/O simply by entering the data in a cell and clicking
it. A response from the external device, if desired, can be read into
the sheet, or the port can be continuously monitored for data from an
external device.

Information is provided for three methods:

1 - OPEN, PRINT/WRITE, CLOSE [EasyTuner - with permission]
2 - API Calls into Kernel32 [Serial IO Only Vers 082.xls – my work]
3 - MSComm [references in the ReadMe]