# FCM or Open UART Interface?

**URL:** <https://forum.sierrawireless.com/t/fcm-or-open-uart-interface/4601>\
**Category:** Open AT\
**Created:** [August 4, 2010, 4:32pm UTC](https://forum.sierrawireless.com/t/fcm-or-open-uart-interface/4601 "2010-08-04T16:32:32Z")\
**Posts on this page:** 1\
**Showing post:** 7

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**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.sierrawireless.com/u/awneil)\
**Post date:** [August 30, 2010, 9:19am UTC](https://forum.sierrawireless.com/t/fcm-or-open-uart-interface/4601/7 "2010-08-30T09:19:28Z")

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> [@rudolfl](#):
>
> It all depends what exactly you try to do.

Very true!  
But I would certainly recommend that anyone try FCM first - and only resort to Open-UART if FCM proves unworkable.

> [@](#):
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> When using FCM, all data goes through OpenAt layer first and

This is true.  
It does impose a performance overhead - so that could be another reason to choose Open-UART

> [@](#):
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> you have to monitor the switch between command and data modes.

True - but you also have to do this for Open-UART.  
See: [AT+WMFM - Inconsistent (and unhelpful) Behaviour](https://forum.sierrawireless.com/t/at-wmfm-inconsistent-and-unhelpful-behaviour/4605/1)

> [@](#):
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> With OpenUART, you are on your own

Very true! 😮  
Not only in terms of the target operation - but also in terms of the awful documentation! 😠

> [@](#):
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> all you get is raw data. You will have to implement your own AT parser.

Surely, if you want to implement a custom AT parser, you could do that using FCM in Data mode?

> [@](#):
>
> We use OpenUART because we do have our own AT parser and use of FCM caused us problems when some commands could not be overwritten and we had same AT command executed by OpenAT

Switching FCM to Data mode bypasses the AT Command processor - can you explain what you mean by this?

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