User's Manual Part 1

MC75 Hardware Interface Description

Strictly confidential / Draft

MC75_V00.190a Page 42 of 91 15.02.2005

3.8 Serial Interface ASC1

MC75 offers a 4-wire unbalanced, asynchronous modem interface ASC1 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 16.

MC75 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 module’s TXD1 signal line

• Port RXD @ application receives data from the module’s RXD1 signal line

GSM module (DCE)

Application (DTE)

TXD

RXD

RTS

CTS

TXD1

RXD1

RTS1

CTS1

Figure 13: Serial interface ASC1

Features

• Includes only the data lines TXD1 and RXD1 plus RTS1 and CTS1 for hardware

handshake.

• On ASC1 no RING line is available. The indication of URCs on the second interface

depends on the settings made with the AT^SCFG command. For details refer to [1].

• Configured for 8 data bits, no parity and 1 or 2 stop bits.

• ASC1 can be operated at bit rates from 300bps to 460800 bps.

• Autobauding TBD.

• Supports RTS1/CTS1 hardware flow control and XON/XOFF software flow control.

Table 7: DCE-DTE wiring of ASC1

DCE DTE V.24

circuit

Pin function Signal direction Pin function Signal direction

103 TXD1 Input TXD Output

104 RXD1 Output RXD Input

105 RTS1 Input RTS Output

106 CTS1 Output CTS Input