User's Manual
Table Of Contents
- Contents
- Figures
- Tables
- Document history
- Introduction
- Product concept
- GSM application interface
- GSM/GPRS operating modes
- Power supply
- Power up / down scenarios
- Automatic GPRS Multislot Class change
- Charging control of the GSM part
- Power saving
- Summary of state transitions (except SLEEP mode)
- RTC backup for GSM part of XT55/56
- Serial interfaces of the XT55/56 GSM part
- Audio interfaces
- SIM interface
- Control signals
- GPS application interface
- GSM and GPS antenna interfaces
- Electrical, reliability and radio characteristics
- Mechanics
- Reference approval
- Example applications
- List of parts and accessories
XT55/56 Hardware Interface Description
Confidential / Released
s
XT55/56_hd_v02.06a Page 55 of 125 17.12.2004
3.9 Serial interfaces of the XT55/56 GSM part
The GSM part of the XT55/56 module offers two unbalanced, asynchronous serial interfaces
conforming to ITU-T V.24 protocol DCE signaling. The electrical characteristics do not
comply with ITU-T V.28. The significant levels are 0V (for low data bit or ON condition) and
2.65V (for high data bit or OFF condition). For electrical characteristics please refer to Table
38. Figure 1 shows the serial interfaces of the XT55/56 module.
The GSM engine 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:
ASC0
• Port TXD @ application sends data to the module’s GSM_TXD0 signal line
• Port RXD @ application receives data from the module’s GSM_RXD0 signal line
ASC1
• Port TXD @ application sends data to module’s GSM_TXD1 signal line
• Port RXD @ application receives data from the module’s GSM_RXD1 signal line
3.9.1 Features supported on the first serial interface of GSM part
(ASC0)
• 8-wire serial interface
• Includes the data lines GSM_TXD0 and GSM_RXD0, the status lines GSM_RTS0 and
GSM_CTS0 and, in addition, the modem control lines GSM_DTR0, GSM_DSR0,
GSM_DCD0 and GSM_RING0.
• It is primarily designed for voice calls, CSD calls, fax calls and GPRS services 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 detailed characteristics see [12].
• The GSM_DTR0 signal will only be polled once per second from the internal firmware of
XT55/56.
• The GSM_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. For further details see
Chapter 3.12.3.
• Autobauding is only selectable on ASC0 and supports the following bit rates: 1200, 2400,
4800, 9600, 19200, 38400, 57600, 115200, 230400 bps.
• Autobauding is not compatible with multiplex mode, see [12].
• ASC0 interface is intended for firmware upgrade of the GSM part