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
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XT55/56_hd_v02.06a Page 68 of 125 17.12.2004
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GSM_RING0
URC
3.12.3 Behavior of the GSM_RING0 line (ASC0 interface only)
The GSM_RING0 line is available on the first serial interface (ASC0). The signal serves to
indicate incoming calls and other types of URCs (Unsolicited Result Code).
Although not mandatory for use in a host application, it is strongly suggested that you
connect the GSM_RING0 line to an interrupt line of your application. In this case, the
application can be designed to receive an interrupt when a falling edge on GSM_RING0
occurs. This solution is most effective, particularly, for waking up an application from power
saving. Note that if the GSM_RING0 line is not wired, the application would be required to
permanently poll the data and status lines of the serial interface at the expense of a higher
current consumption. Therefore, utilizing the GSM_RING0 line provides an option to
significantly reduce the overall current consumption of your application.
The behavior of the GSM_RING0 line varies with the type of event:
• When a voice call comes in the GSM_RING0 line goes low for 1s and high for another
4s. Every 5 seconds the ring string is generated and sent over the GSM_RXD0 line.
If there is a call in progress and call waiting is activated for a connected handset or
handsfree device, the GSM_RING0 line switches to ground in order to generate acoustic
signals that indicate the waiting call.
Figure 23: Incoming voice call
• Likewise, when a Fax or data call is received, GSM_RING0 goes low. However, in
contrast to voice calls, the line remains low. Every 5 seconds the ring string is generated
and sent over the GSM_RXD0 line.
Figure 24: Incoming data call
• All types of Unsolicited Result Codes (URCs) also cause the
GSM_RING0 line to go low, however for 1 second only.
For example, XT55/56 may be configured to output a URC
upon the receipt of an SMS. As a result, if this URC type
was activated with AT+CNMI=1,1, each incoming SMS
causes the GSM_RING0 line to go low. See [1] for detailed
information on URCs.
Figure 25: URC transmission
5s
GSM_RING0
Ring
string
Ring
string
Ring
string
5s
4s
GSM_RING0
4s
1s
1s
1s
Ring
string
Ring
string
Ring
string