5. HC15 AT COMMAND INTERPRETER
After successful installation of the HC15 driver package, the physical USB interface of the module is represented in the operating system by two virtual interfaces, each assigned to a virtual COM port of its own:
• Modem interface:
This interface is referred to as "Modem" if queried with AT^SQPORT. In the quick reference tables it is named USB0-MDM. In Windows XP, it will show up as "Siemens HSDPA USB Modem" in the Windows Device Manager, under Modems. The COM port number automatically assigned by Windows during the installation can be gathered from the Modems property page.
The modem interface is intended particularly for data transmission (HSDPA, GPRS, CSD or FAX) established over a dial-up connection. Using AT commands on this interface is not recommended, except for data call related commands like ATD or ATO.
URCs relevant for data calls (RING, NO CARRIER) are issued on the modem interface, all other URCs normally only on the application interface.
• Application interface:
This port is referred to as "Application" if queried with AT^SQPORT. In the quick reference tables it is named USB0-APP. In Windows XP, it will show up as "Siemens HSDPA USB Com Port" in the Windows Device Manager, under Ports (COM&LPT), along with the COM port number automatically assigned by Windows.
The application interface is designed especially for controlling the HC15, i.e. for entering AT commands, receiving URCs, or sending and receiving short messages. It cannot be used as data interface for HSDPA, GPRS, CSD or FAX.
Please note that URCs are normally indicated only on this interface, no matter which of the two interfaces was used to send the AT commands for activating their presentation. This URC management scheme is the default configuration recommended for a typical MTX-H15 application.
If you need to operate the MTX-H15 from both interfaces at a time, bear in mind that both are handled by the same AT command interpreter. As a result, AT commands entered on both interfaces are not executed in parallel but sequentially, one after the other. So, an AT command issued on one interface will be buffered on this interface to be executed after the other interface has completed processing earlier AT command(s). The buffered command string is not echoed, but will be indicated when executed.
When a dial-up connection is established over the modem interface, the application interface can be used simultaneously for any control functions. This eliminates the need for the user to enter AT commands, such as +++ and ATO, to switch back and forth between command and online mode when working on one interface only. Yet, it should be noted that the dial-up connection disables the echo on both interfaces, due to the initialization strings typically set by modems. The echo can be re-activated by executing ATE1.
See MTX-H15 quick user guide for a complete step by step installation process.
