# FCM set data receive amount

**URL:** <https://forum.sierrawireless.com/t/fcm-set-data-receive-amount/4283>\
**Category:** Open AT\
**Created:** [March 11, 2010, 9:30am UTC](https://forum.sierrawireless.com/t/fcm-set-data-receive-amount/4283 "2010-03-11T09:30:17Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![julyate](https://avatars.discourse-cdn.com/v4/letter/j/8e7dd6/32.png) [@julyate](https://forum.sierrawireless.com/u/julyate)\
**Post date:** [March 11, 2010, 9:30am UTC](https://forum.sierrawireless.com/t/fcm-set-data-receive-amount/4283/1 "2010-03-11T09:30:17Z")

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Good day,

I want to interface my Wavecom chip with an external device via UART2. The data packets from the device are always 6 bytes long, is there any way to tell the FCM to only call the datahandler once 6 bytes have been read?

Best regards

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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:** [March 11, 2010, 10:44am UTC](https://forum.sierrawireless.com/t/fcm-set-data-receive-amount/4283/2 "2010-03-11T10:44:15Z")

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No, there isnt.

FCM will call the data handler when it feels like it, and will tell you how much data is available.

I suggest a State Machine to allow you to re-assemble the frames in case they get split…

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**Author:** ![julyate](https://avatars.discourse-cdn.com/v4/letter/j/8e7dd6/32.png) [@julyate](https://forum.sierrawireless.com/u/julyate)\
**Post date:** [March 13, 2010, 9:23pm UTC](https://forum.sierrawireless.com/t/fcm-set-data-receive-amount/4283/3 "2010-03-13T21:23:44Z")

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Thank you for your reply, I implemented something of the sort to work around it.