Send data directly from COM3 to Excel

I’m sorry you’re dealing with that freezing issue—that "blue spinning loop" is a classic sign of a tight loop consuming all CPU resources or a blocking API call.

To give you a fix that actually works, I really need a bit more information from you:

1. OS & Excel: (e.g., Windows 11 + Excel 365 64-bit)
2. Device: What is connected to COM3? (Make/Model helps find the correct Baud Rate).
3. Settings: What Baud Rate, Data Bits, Parity, and Stop bits does the device use? (Check the device manual or Device Manager > Port Settings > Advanced).
4. Location: Is the file on a local drive or Network/OneDrive? (Network latency can exacerbate freezing).

However, I can try to tell you why it's hanging right now and how to stop it:

Culprit 1: The "Busy Wait" Loop
The current code uses DoEvents without a pause. This spins the CPU at 100%.

• Fix: Add a micro-sleep. Replace DoEvents with:

DoEvents

Sleep 50 ' Requires declaring the Sleep API (see below)

Culprit 2: Missing COM Port Configuration (Most Likely)
The code opens COM3 but doesn't tell Windows how to talk to it (Baud rate, etc.). If the device is set to 9600 baud and Windows defaults to a different speed, data is garbage or empty, and the read loop never exits.

• Fix: We must add SetCommState and SetCommTimeouts API calls to configure the port immediately after opening it.

Culprit 3: Blocking ReadFile
The ReadFile call is "blocking." If the device doesn't send data instantly, Excel freezes waiting for it.

• Fix: We must set a Read Timeout (e.g., 100ms) using SetCommTimeouts. If no data arrives in 100ms, the function returns, and the loop tries again without crashing.

Immediate "Safe" Code Snippet (64-bit compatible with Timeouts):

Since you are crashing, try this minimal version. It includes the Sleep API to prevent freezing and basic error handling.

' Add this at the very top of the module
Declare PtrSafe Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)

' ... [Keep your existing Declarations for CreateFile, ReadFile, etc.] ...

' Add Timeout Structures and APIs
Type COMMTIMEOUTS
    ReadIntervalTimeout As Long
    ReadTotalTimeoutMultiplier As Long
    ReadTotalTimeoutConstant As Long
    WriteTotalTimeoutMultiplier As Long
    WriteTotalTimeoutConstant As Long
End Type
Declare PtrSafe Function SetCommTimeouts Lib "kernel32" (ByVal hFile As LongPtr, ByVal lpCommTimeouts As LongPtr) As Long
Declare PtrSafe Function GetCommTimeouts Lib "kernel32" (ByVal hFile As LongPtr, ByVal lpCommTimeouts As LongPtr) As Long

' Modified Open Function with Timeouts
Function OpenSerialPort(portName As String) As Boolean
    hComm = CreateFile(portName, GENERIC_READ Or GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)
    If hComm = INVALID_HANDLE_VALUE Then
        OpenSerialPort = False
        Exit Function
    End If
    
    ' SET TIMEOUTS (Crucial for preventing hangs)
    Dim timeouts As COMMTIMEOUTS
    timeouts.ReadIntervalTimeout = 0
    timeouts.ReadTotalTimeoutMultiplier = 0
    timeouts.ReadTotalTimeoutConstant = 100 ' 100ms read timeout
    SetCommTimeouts hComm, timeouts
    
    OpenSerialPort = True
End Function

' Modified Read Function
Function ReadSerialPort() As String
    Dim buffer As String * 1024
    Dim bytesRead As Long
    Dim result As Long
    
    ' Non-blocking check approach is complex, so we rely on the timeout set above
    result = ReadFile(hComm, buffer, Len(buffer), bytesRead, ByVal 0&)
    
    If result <> 0 And bytesRead > 0 Then
        ReadSerialPort = Left(buffer, bytesRead)
    Else
        ReadSerialPort = "" ' Timeout or empty
    End If
End Function

' Modified Loop
Sub ReadFromSerialPort()
    Dim data As String
    Dim row As Long
    
    If Not OpenSerialPort("COM3") Then
        MsgBox "Failed to open COM3. Check Device Manager."
        Exit Sub
    End If
    
    row = 2
    
    Do
        data = ReadSerialPort()
        If data <> "" Then
            ThisWorkbook.Sheets(1).Cells(row, 1).Value = Now
            ThisWorkbook.Sheets(1).Cells(row, 2).Value = data
            row = row + 1
        End If
        
        ' PREVENT FREEZE: Yield CPU and Sleep
        DoEvents
        Sleep 50 ' 50ms pause
        
        ' Optional: Check if Esc key is pressed to stop
        If GetAsyncKeyState(vbKeyEscape) Then Exit Do
    Loop
    
    CloseSerialPort
End Sub

If you share the device details/settings requested above, I can provide the full SetCommState (Baud rate) code as well.

In the meantime, I strongly recommend downloading PuTTY, selecting "Serial," entering COM3 and the correct Baud Rate, and seeing if text appears. If it doesn't appear in PuTTY, the issue is drivers/cables, not Excel.

I hope this information is helpful to you.