SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
System description
Page 57 of 217
Wake up via data reception
The UART wake up via data reception consists of a special configuration of the module
TXD
input line that
causes the system wake-up when a low-to-high transition occurs on the
TXD
input line. In particular, the UART
is enabled and the module switches from the low power idle mode to active mode within ~20 ms from the first
character received: this is the system “wake up time”.
As a consequence, the first character sent by the DTE when the UART is disabled (i.e. the wake up character) is
not a valid communication character even if the wake up via data reception configuration is active, because it
cannot be recognized, and the recognition of the subsequent characters is guaranteed only after the complete
system wake-up (i.e. after ~20 ms).
The UART wake up via data reception configuration is active in the following cases:
On SARA-G3 series, the
TXD
input line is configured to wake up the system via data reception if:
o
AT+UPSV=1 is set with HW flow control disabled
o
AT+UPSV=2 is set with HW flow control disabled, and the
RTS
line is set OFF
On SARA-U2 series, the
TXD
input line is configured to wake up the system via data reception only if
o
AT+UPSV=1 is set with hardware flow control disabled
On SARA-U2 series, the UART wake up via data reception configuration is not active on the
TXD
input,
and therefore all the data sent by the DTE is lost, if:
o
AT+UPSV=2 is set with HW flow control disabled, and the
RTS
line is set OFF
o
AT+UPSV=3 is set, regardless of the HW flow control setting, and the
DTR
line is set OFF
Figure 29 and Figure 30 show examples of common scenarios and timing constraints:
AT+UPSV=1 power saving configuration is active and the timeout from last data received to idle mode start
is set to 2000 frames (AT+UPSV=1,2000)
Hardware flow control is disabled
Figure 29 shows the case where the module UART is disabled and only a wake-up is forced. In this scenario the
only character sent by the DTE is the wake-up character; as a consequence, the DCE module UART is disabled
when the timeout from last data received expires (2000 frames without data reception, as the default case).
OFF
ON
DCE UART is enabled for 2000 GSM frames (~9.2 s)
time
Wake up time: ~20 ms
time
TXD input
Wake up character
Not recognized by DCE
UART
OFF
ON
Figure 29: Wake-up via data reception without further communication
