HE920 Hardware User Guide
1vv0301014 Rev.9 – 2014-01-23
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
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Page 50 of 84
7.1.
Reset Signal(Module Restart)
Signal
Function
I/O
PAD Number
RESET*
Phone reset
(restart)
I
AP1
RESET is used to reset the HE920 module. Whenever this signal is pulled low HE920 is reset
(restart). When the device is reset it stops all operations. After the release of the reset HE920
is unconditionally shut down, without doing any detach operations from the network where it
is registered. This behavior is not a proper shutdown because the device is requested to issue a
detach request on turn off. For this reason, the Reset signal must not be used for normally
shutting down the device, but only as an emergency exit in the rare case the device remains
stuck waiting for some network response.
The RESET is internally controlled on start-up to achieve always a proper power-on reset
sequence. There is no need to control this pin on start-up. It may only be used to reset a
device already on that is, not responding to any command.
NOTE:
Do not use this signal to power off HE920. Use the ON/OFF signal to perform this function
or the AT#SHDN command.
Reset Signal Operating levels:
Signal
Min
Max
RESET Input high
1.5V*
2.1V
RESET Input low
0V
0.2V
* This signal is internally pulled up so the pin can be left floating if not used.
If unused, this signal may be left unconnected. If used, it must always be connected with an
open collector transistor to permit the internal circuitry the power on reset and under voltage
lockout functions.
NOTE:
In order to avoid a back powering effect it is recommended to avoid having any HIGH logic
level signal applied to the digital pins of the module when is powered OFF or during an
ON/OFF transition.
