> 1.9 | Second Serial Interface ASC1

> The second serial interface ASC1 is designed as an auxiliary interface for applications which need multiple parallel access to the module (e.g. to query status information on ASC1 while a data connection is in progress on ASC0). Therefore the second interface provides only limited functionality:

> • | Multiplex mode according to GSM 07.10 and 3G TS 27.010 is not supported on ASC1.

> • | DTR, DSR, DCD, RING hardware lines do not exist on ASC1. AT commands for controlling the behavior of these lines (AT&D, AT&C, AT&S) can be used but will have no effect.

> • | CSD calls are not supported on ASC1.

> • | Fax calls are not supported on ASC1.

> • | When you set up packet switched connections take care that your application uses only AT commands, parameters and signal lines supported on the ASC1 interface. For example, keep in mind that Microsoft Dial-up connections are typically trying to request the DCD line status and that common modem drivers use to send commands such as AT+CBST, ATS7 (not supported on ASC1).

> • | No Autobauding. The hardware is not capable of automatically detecting the baudrate on this interface, so the AT command which selects autobauding (AT+IPR=0) is not allowed and returns ERROR.

> ASC1 is disabled when the multiplexer is enabled on the first serial interface ASC0. Yet, both ASC1 and the multiplexer channel 2 are using the same parameters, and thus, the same user defined profile (if any). As a result, a user profile stored on multiplexer channel 2 takes effect on ASC1 after closing the multiplexer and starting up ASC1. Likewise, a user profile stored on ASC1 will be loaded on multiplexer channel 2.
> This may be a problem when ASC1 is not connected, but flow control (for example AT\Q1 or AT\Q3) is stored to the user profile on the multiplexer channel 2. In this case, flow control takes effect on ASC1, when the multiplexer is switched off. If then for example a large amount of URCs is generated, their transmission might be stopped due to the flow control. To avoid this problem we recommend that you do not activate flow control on multiplexer channel 2 when you set up a user profile with AT&W.