> 3.10 | Serial Interface ASC0

> TC65 offers an 8-wire unbalanced, asynchronous modem interface ASC0 conforming to ITU-T V.24 protocol DCE signalling. The electrical characteristics do not comply with ITU-T V.28. The significant levels are 0V (for low data bit or active state) and 2.9V (for high data bit or inactive state). For electrical characteristics please refer to Table 30.
> TC65 is designed for use as a DCE. Based on the conventions for DCE-DTE connections it communicates with the customer application (DTE) using the following signals:

> • | Port TXD @ application sends data to the module’s TXD0 signal line

> • | Port RXD @ application receives data from the module’s RXD0 signal line

> Figure 17: Serial interface ASC0
> Features:

> • | Includes the data lines TXD0 and RXD0, the status lines RTS0 and CTS0 and, in addition, the modem control lines DTR0, DSR0, DCD0 and RING0.

> • | ASC0 is primarily designed for controlling voice calls, transferring CSD, fax and GPRS data and for controlling the GSM engine with AT commands.

> • | Full Multiplex capability allows the interface to be partitioned into three virtual channels, yet with CSD and fax services only available on the first logical channel. Please note that when the ASC0 interface runs in Multiplex mode, ASC1 cannot be used. For more details on Multiplex mode see [10].

> • | The DTR0 signal will only be polled once per second from the internal firmware of TC65.

> • | The RING0 signal serves to indicate incoming calls and other types of URCs (Unsolicited Result Code). It can also be used to send pulses to the host application, for example to wake up the application from power saving state. See [1] for details on how to configure the RING0 line by AT^SCFG.

> • | By default, configured for 8 data bits, no parity and 1 stop bit. The setting can be changed using the AT command AT+ICF and, if required, AT^STPB. For details see [1].

> • | ASC0 can be operated at fixed bit rates from 300 bps to 460800 bps.

> • | Autobauding supports bit rates from 1200 to 460800 bps.

> • | Autobauding is not compatible with multiplex mode.

> • | Supports RTS0/CTS0 hardware flow control and XON/XOFF software flow control.

> Table 15: | DCE-DTE wiring of ASC0

> V.24 circuit | DCE | DTE
> Pin function | Signal direction | Pin function | Signal direction
> 103 | TXD0 | Input | TXD | Output
> 104 | RXD0 | Output | RXD | Input
> 105 | RTS0 | Input | RTS | Output
> 106 | CTS0 | Output | CTS | Input
> 108/2 | DTR0 | Input | DTR | Output
> 107 | DSR0 | Output | DSR | Input
> 109 | DCD0 | Output | DCD | Input
> 125 | RING0 | Output | RING | Input