USB VCP Information

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Whilst the Z-text SMS modem is USB, it appears as a Virtual COM Port (VCP) to the host PC.

Like any VCP, this can only be accessed by one program at a time, and the VCP cannot be shared with another application. An application that has been minimized, still has 100% control of the VCP. If the Z-text SMS modem will be used with a third party application, the Z-text application software will need to be removed from the start menu. If the Z-text application reports "modem not found" this is normally due to another program having control of the COM port, or the USB cable being connected after the application has been loaded.

Prior to using a third party application such as environmental or network monitoring software, it is recommended that the supplied Z-text application or a terminal emulator is used to confirm that the modem is correctly installed and sending messages.

Before using a terminal program, make a note of the COM port the modem has been assigned. On a windows system this can be found in Device Manager.

The terminal program settings are 2400 8N1, you will also need to select the "echo typed characters locally" option, or send the ATE0 AT command to the modem. The ATI0 command will return the modems product information and firmware version.

The Z-text SMS modem USB device is the CP2101 manufactured by Silicon Laboratories (SiLabs).

The SMS modem has an NTS Telecom VID & PID which is suitable for the supplied Windows drivers. For use with Linux or MAC USB drivers, the modem will need to be ordered with a SiLabs VID/PID suitable for use with these drivers. A Windows utility to change the VID & PID is available on request.

The SiLabs VID & PID also allow the use of the SiLabs WHQL Certified drivers.

Further information on the SiLabs drivers can be found here

NTS Telecom VID 14B5 (5301)

NTS Telecom PID 5A74 (23156)

SiLabs VID 10C4 (4292)

SiLabs PID EA61 (60001)

The COM port number is allocated by Windows on device installation, and can be found from Device Manager under the 'Ports ( COM & LPT )' entry. It is possible that the port could be greater than 9 if many port numbers are already allocated ( eg. Bluetooth adaptors often take up a lot of ports ), which can cause a problem if the port is not opened correctly. Calling CreateFile to open "COM4" will work fine, but "COM10" will not. Using the form "\\.\COM10" will work correctly for all port numbers.

Microsoft has an article about this problem here

If the modem has been installed but not currently connected to the computer, it will not normally be displayed in Device Manager. A useful utility from Winguides enables you to display unconnected USB devices.

Microsoft also provide information on viewing hidden and non-present devices in Device Manager.