# xbee rx tx buffer size and message size **URL:** \ **Category:** XBee & XBee Gateway\ **Tags:** xbee-api-mode, xbee3, xbee\ **Created:** [February 15, 2021, 10:46am UTC](https://forums.digi.com/t/xbee-rx-tx-buffer-size-and-message-size/22207 "2021-02-15T10:46:51Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![naki](https://avatars.discourse-cdn.com/v4/letter/n/f9ae1b/32.png) [@naki](https://forums.digi.com/u/naki)\ **Post date:** [February 15, 2021, 10:46am UTC](https://forums.digi.com/t/xbee-rx-tx-buffer-size-and-message-size/22207/1 "2021-02-15T10:46:51Z")
hey forum I spend some time looking though documentation but I can not find the answer to what I am look at. I am using 802.15.4 and no API right now on the xbee s2c. what I found is that the tx uart buffer has 153 bytes and the rx has 140 bytes. I can transmit both ways 10 characters, lets say “0123456789” which should be 10bytes plus start and stop bits. Which is less that 140 bytes. I have DB 9600, 8N1. I can find the frame size when using the API - it stays 4 bytes - n, but haven’t tested it yet. so what I am missing, or where did I went wrong? thanks in advance ---
**Author:** ![mvut](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.digi.com/mvut/32/31_2.png) [@mvut](https://forums.digi.com/u/mvut)\ **Post date:** [February 15, 2021, 11:29am UTC](https://forums.digi.com/t/xbee-rx-tx-buffer-size-and-message-size/22207/2 "2021-02-15T11:29:25Z")
API frames include more than 4 bytes. There is the following in the frame: Start delimiter Length 2 bytes Frame type Frame ID 64 bit dest. address option byte Data payload Checksum ---
**Author:** ![naki](https://avatars.discourse-cdn.com/v4/letter/n/f9ae1b/32.png) [@naki](https://forums.digi.com/u/naki)\ **Post date:** [February 16, 2021, 7:49am UTC](https://forums.digi.com/t/xbee-rx-tx-buffer-size-and-message-size/22207/3 "2021-02-16T07:49:45Z")
OK I figured I out. The data payload can host up to 256 bytes. The Frame Interpreter tool from XTCU helped. It shows the entire Frame and you an also see your payload and in combination with the Frame Generator documentation makes sense again.