# Speed in API mode

**URL:** <https://forums.digi.com/t/speed-in-api-mode/1859>\
**Category:** XBee - 802.15.4\
**Created:** [June 15, 2012, 5:00pm UTC](https://forums.digi.com/t/speed-in-api-mode/1859 "2012-06-15T17:00:22Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Checkfluid](https://avatars.discourse-cdn.com/v4/letter/c/977dab/32.png) [@Checkfluid](https://forums.digi.com/u/Checkfluid)\
**Post date:** [June 15, 2012, 5:00pm UTC](https://forums.digi.com/t/speed-in-api-mode/1859/1 "2012-06-15T17:00:22Z")

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Hi All,

I am using an XBee in API mode, in a timing critical application. I have noticed that when using the XBee as a serial replacement, the transfer occurs almost instantly, however when I transmit an API frame of 2 bytes, the transfer takes about 1/4 to 1/2 a second.

Is this due to the way that the API mode works, or is this a limitation of my microcontroller? Also, in API mode is there any way of boosting the speed (possibly by increasing the baud rate or disabling ACKs)?

Thanks in advance!

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**Author:** ![lynnl](https://avatars.discourse-cdn.com/v4/letter/l/22d042/32.png) [@lynnl](https://forums.digi.com/u/lynnl)\
**Post date:** [June 18, 2012, 3:08pm UTC](https://forums.digi.com/t/speed-in-api-mode/1859/2 "2012-06-18T15:08:56Z")

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Hmm, you mean TX/sending 2 bytes of ‘RF data’ with an frame 0x10 or 0x11? So 1 byte or 3 bytes is faster?

I have no trouble sending a dozen frames a second (but I use ZigBee or DigiMesh), and I know of customers expecting a 50msec latency with 802.15.4 (note: Zigbee won’t support this! but this is 802.15.4/S1 forum, not ZigBee forum).

You are using direct transmission, correct?

The TX options include disabling the ACK.

I have never seriously used 802.15.4, but perhaps either 0x10 or 0x11 is faster?