SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26 System description
Page 52 of 217
RI signal behavior
The RI module output line is set by default to the OFF state (high level) at UART initialization. Then, during an
incoming call, the RI line is switched from the OFF state to the ON state with a 4:1 duty cycle and a 5 second
period (ON for 1 s, OFF for 4 s, see Figure 26), until the DTE attached to the module sends the ATA string and
the module accepts the incoming data call. The RING string sent by the module (DCE) to the serial port at
constant time intervals is not correlated with the switch of the RI line to the ON state.
Figure 26: RI behavior during an incoming call
The RI line can notify an SMS arrival. When the SMS arrives, the RI line switches from OFF to ON for 1 second
(see Figure 27), if the feature is enabled by the AT+CNMI command (see the u-blox AT Commands Manual [3]).
Figure 27: RI behavior at SMS arrival
This behavior allows the DTE to stay in power saving mode until the DCE related event requests service.
For SMS arrival, if several events coincidently occur or in quick succession each event independently triggers the
RI line, although the line will not be deactivated between each event. As a result, the RI line may stay to ON for
more than 1 s.
If an incoming call is answered within less than 1 second (with ATA or if auto-answering is set to ATS0=1) than
the RI line is set to OFF earlier.
As a result:
RI line monitoring cannot be used by the DTE to determine the number of received SMSes.
For multiple events (incoming call plus SMS received), the RI line cannot be used to discriminate the two
events, but the DTE must rely on the subsequent URCs and interrogate the DCE with proper commands.
The RI line can additionally notify all the URCs and all the incoming data (PPP, Direct Link, sockets, FTP), if the
feature is enabled by the AT+URING command (for more details, see the u-blox AT Commands Manual [3]): the
RI line is asserted when one of the configured events occur and it remains asserted for 1 second unless another
configured event will happen, with the same behavior described in Figure 27.
The AT+URING command for the notification of all the URCs and all the incoming data (PPP, Direct Link,
sockets, FTP) over the RI line output is not supported by SARA-G3 modules.
1s
time [s]
151050
RI ON
RI OFF
Call incomes
1s
time [s]
151050
RI ON
RI OFF
Call incomes
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