User Manual
Table Of Contents
- 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 / Preliminary
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XT55/56_hd_v02.96 Page 33 of 125 18.08.2005
Assertion of GSM_CTS indicates that the module is ready to receive data from the host
application. In addition, if configured to a fixed bit rate (AT+IPR0), the module will send the
URC “^SYSSTART” which notifies the host application that the first AT command can be sent
to the module. The duration until this URC is output varies with the SIM card and may take a
couple of seconds, particularly if the request for the SIM PIN is deactivated on the SIM card.
Please note that no “^SYSSTART” URC will be generated if autobauding (AT+IPR=0) is
enabled.
To allow the application to detect the ready state of the module we recommend using
hardware flow control which can be set with AT\Q or AT+ICF (see [1] for details). The default
setting of XT55/56 is AT\Q0 (no flow control) which shall be altered to AT\Q3 (RTS/CTS
handshake). If the application design does not integrate RTS/CTS lines the host application
shall wait at least for the “^SYSSTART” URC. However, if the URCs are neither used (due to
autobauding) then the only way of checking the module’s ready state is polling. To do so, try
to send characters (e.g. “at”) until the module is responding.
3.3.1.2 Timing of the Ignition Process
When designing your application platform take into account that powering up the GSM part of
the XT55/56 module requires the following steps.
• The ignition line cannot be operated until V
GSM_BATT+
passes the level of 3.0V.
• The ignition line shall not be operated earlier than 10ms after the last falling edge of
GSM_VDD.
• 10ms after V
GSM_BATT+
has reached 3.0V the ignition line can be switched low. The
duration of the falling edge must not exceed 1ms.
• Another 100ms are required to power up the module.
• Ensure that V
GSM_BATT+
does not fall below 3.0V while the ignition line is driven. Otherwise
the module cannot be activated.
• If the GSM_VDDLP line is fed from an external power supply as explained in Chapter 3.8,
the GSM_IGT line is HiZ before the rising edge of GSM_BATT+.
Figure 5: Timing of power-on process if GSM_VDDLP is not used
3.0V
0V
GSM_BATT+
min. 100ms
max. 1ms
10ms
GSM_IGT
HiZ
HiZ