Public Function A2DValue( _
    ByVal ChannelIndex As Integer) As Integer

'Read data from  a/d converter MAX187

Dim BitIndex As Integer
Dim TempData As Integer
Dim NbrLoops As Integer

With frmMain.SerialPort(ChannelIndex)
    'Start convert (CS-bar high to low)
    .RTSEnable = True 'CS-bar low
    Do While .DSRHolding
        DoEvents
        NbrLoops = NbrLoops + 1
        If NbrLoops >= 100 Then
            Exit Function
        End If
    Loop
    'Read data bits from msb to lsb (Clock MAX187 SCLK 12 times)
    For BitIndex = 11 To 0 Step -1
        .DTREnable = False 'SCLK high
        .DTREnable = True 'SCLK low
        'read bit value
        TempData = TempData + Abs(Not .DSRHolding) * 2 ^ BitIndex
    Next
    'One more clock cycle
    .DTREnable = False 'SCLK high
    .DTREnable = True 'SCLK low
    'End convert (CS-bar low to high)
    .RTSEnable = False 'CS-bar high
End With
'returned value
A2DValue = TempData

End Function