User's Guide

LM940 HW Design Guide
1VV0301352 Rev. 2 Page 35 of 68 2017-07-19
Information – To check if the LM940 has completely powered on,
LM940 and the host must be connected via USB. When USB driver
completely loaded, the module has completely powered on and is
ready to accept AT commands.
Information – During SW initialization of the LM940, the SW configures
all pins and interfaces to their desired mode. When VREG_L6_1P8
goes high, this indicates that the initialization of all I/O pins is
completed.
Information – Active low signals are labeled with a name that ends with
“_N”
Information – 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 it is powered OFF or during an ON/OFF transition.
Power Off
The LM940 module can be shut down by a software command.
When a shutdown command is sent, LM940 goes into the Finalization state and at the end
of the finalization process shuts down VREG_L6_1P8. The duration of the finalization
state can differ according to the current situation of the module, so a value cannot be
defined.
Usually, it will take more than 12 seconds from sending a shutdown command until
reaching a complete shutdown. The DTE should monitor the status of VREG_L6_1P8 to
observe the actual power-off.
Information – To completely shut down the LM940 module, the
W_DISABLE_N pin must be asserted low.
Otherwise, the LM940 will turn on again after shut down.