How to Detect Valid COM Ports

Keywords:     pComOpen	 pGetLastError(1)

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Question:

I want to be able to search for a modem on COM ports 1-4. If a modem isn't found on any of those ports, I'll display a message to that effect. But if I get all the way to COM4 without finding a modem, I get a WIL error I don't understand. Here's the relevant part of the batch:

display(3,"Please wait...","Looking for modem on COM4")
port=pComOpen("COM4",0,9600,"8N1","XONXON")
pPutString(port,"ATZ")
pPutString(port,@cr)
if pWaitFor(port,"OK","",0,3000)==0
pComClose(port,-1)
goto NO_MODEM
else
ComPort=4
goto SHOWCOMPORT
endif
goto NO_MODEM

The error message is:

WIL Extender Error---------
port=pComOpen("COM4",0,9600,"8N1","XONXON")
Winbatch 32.97D
WIL Version 2.4dbp

There is no number in the Error Message, only a series of dashes. The PC on which this error message was generated does not have a COM4, but I've tested the same script on a PC that does, and get the same message. Is there a way to check either the validity of a COM port, or for an error message from pComOpen() ?

Answer:

Try the following code instead...

;=======================snip===========================
DirChange("c:\program files\WinBatch\system")
AddExtender("wwser34I.dll")
debug(1)
display(3,"Please wait...","Looking for modem on COM4")
ErrorMode(@off)
port=pComOpen("COM4",0,9600,"8N1","XONXON")
ErrorMode(@cancel)
code=pGetLastError(1)
Message("Open err msg",code)
if port==- then exit
pPutString(port,"ATZ")
pPutString(port,@cr)
if pWaitFor(port,"OK","",0,3000)==0
pComClose(port,-1)
goto NO_MODEM
else
ComPort=4
goto SHOWCOMPORT
endif
goto NO_MODEM
;=======================================================

After capturing the error code, do a StrIndex to test whether the code indicated an invalid port. Works great.

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Article ID:   W12570

Filename:   Detecting Valid COM Ports.txt