LM940 Hardware Design Guide
1VV0301352 Rev. 18 Page 35 of 75 2022-01-04
Note: To verify if the LM940 has powered up properly, please check
through one of two conditions below:
(1) LM940 and the host should be connected via USB. When USB
driver is completely loaded, the module has powered on without
problems and is ready to accept AT commands.
(2) Monitoring Boot OK (Shutdown Indicator). To use Boot OK
(Shutdown Indicator), Boot OK(Shutdown Indicator) function must be
enabled through AT#SHDNIND. (Refer to the AT User Guide
document)
Active low signals are labeled with a name that ends with “_N”.
Note: 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
Power off the device can be done in three different ways:
• Graceful Shutdown by USB AT command AT#SHDN
• Fast Shutdown by GPIO triggered or USB AT command AT#FASTSHDN
• Unconditional Shutdown using the SYSTEM_RESET_N
6.3.1. Graceful Shutdown
To shutdown the LM940 module more safely, host can use the graceful shutdown
function.
The graceful shutdown can be triggered by:
• AT command via USB
6.3.1.1. Graceful Shutdown by AT Command
To gracefully shutdown the LM940 module,
First, shutdown AT command must be sent via a USB communication.
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