LM940 Hardware Design Guide
1VV0301352 Rev. 18
Page 34 of 75
2022-01-04
Not Subject to NDA
Note: To turn on the LM940 module, the SYSTEM_RESET_N pin must
not be asserted low. In addition, in case of LM940 1.0, W_DISABLE_N
muse is not asserted low.
6.2.1.
Initialization and Activation State
After turning on the LM940 module, the LM940 is not instantly activated because the SW
initialization process takes some time to complete.
For this reason, it is recommended not to communicate with the LM940 during the
Initialization phase.
Boot OK (Shutdown Indicator) goes high at the time of AT command is available via USB.
But this does not mean that it works fully.
As soon as the AT command interface is accessible via USB port, Boot OK line transitions
to high but this does not imply that the device is fully operational yet.
One of GPIO pins can be configured as Shutdown indicator by means of AT#SHDNIND
command: in that case, that GPIO will also work as Boot OK line when the module is
booting.
Please refer to AT Commands Reference Guide for additional details.
In general, as shown in below figure, the LM940 becomes fully operational (in the
Activation state) at least 35 seconds after the VBATT is supplied.
Figure 4: LM940 Initialization and Activation