# Disable AT commands before user application

**URL:** <https://forum.sierrawireless.com/t/disable-at-commands-before-user-application/5673>\
**Category:** Open AT\
**Created:** [June 21, 2012, 3:14pm UTC](https://forum.sierrawireless.com/t/disable-at-commands-before-user-application/5673 "2012-06-21T15:14:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![msmoczynski](https://avatars.discourse-cdn.com/v4/letter/m/57b2e6/32.png) [@msmoczynski](https://forum.sierrawireless.com/u/msmoczynski)\
**Post date:** [June 21, 2012, 3:14pm UTC](https://forum.sierrawireless.com/t/disable-at-commands-before-user-application/5673/1 "2012-06-21T15:14:54Z")

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Hi.  
I have a product based on SL6087 SW modem. I’d like to disable AT command execution from the power up moment. There is a piece of code which changes FCM flow in the application using “adl\_fcmSwitchV24State” function and it works great, but there is a slight moment before application start, when AT commands are handled, so it is possible to send “AT+WOPEN=0” command to disable application and “hack” the device. Desired communication scheme is described as follows:  
UART1 - own protocol, AT commands after authentication (software switch using FCM)  
UART2 - not supported by hardware  
USB - not supported by hardware.

Is it possible disable UART1 and enable it within application AFTER fcm switch?  
I would appreciate any help.

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**Author:** ![zafer](https://avatars.discourse-cdn.com/v4/letter/z/439d5e/32.png) [@zafer](https://forum.sierrawireless.com/u/zafer)\
**Post date:** [June 22, 2012, 8:05am UTC](https://forum.sierrawireless.com/t/disable-at-commands-before-user-application/5673/2 "2012-06-22T08:05:03Z")

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Remember that even if you switch your modem to data mode with adl\_fcmSwitchV24State function, external applications can still switch it back to AT mode with “+++” sequence. So you should control your uart handler to keep being in data mode always.  
But i think you can not prevent any external application attemps breaking the data mode with “+++”. This will bother your open at application. You can also think about phisical protection for uart port insead.

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**Author:** ![msmoczynski](https://avatars.discourse-cdn.com/v4/letter/m/57b2e6/32.png) [@msmoczynski](https://forum.sierrawireless.com/u/msmoczynski)\
**Post date:** [June 22, 2012, 3:12pm UTC](https://forum.sierrawireless.com/t/disable-at-commands-before-user-application/5673/3 "2012-06-22T15:12:05Z")

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Thanks zafer for the heads up about ‘+++’ sequence.

Is it possible to subscribe to FCM after opening with adl\_OpenDevice port closed with +WMFM? What I want to achieve is:

1. Close UART1 from UART2/3 with AT+WMFM=0,0,1 during production,
2. Disable WDWL and WOPEN with adl security functions,
3. Open UART1 in application with adl\_OpenDevice,
4. Subscribe to FCM to be able to switch between data and AT commands on demand after authentication.

Thanks for any clues.  
Regards