# \[HL8518\] 921600 baudrate and CMUX **URL:** \ **Category:** Legacy HL Series\ **Created:** [July 4, 2019, 7:14pm UTC](https://forum.sierrawireless.com/t/hl8518-921600-baudrate-and-cmux/16893 "2019-07-04T19:14:54Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![roel0](https://avatars.discourse-cdn.com/v4/letter/r/eb8c5e/32.png) [@roel0](https://forum.sierrawireless.com/u/roel0)\ **Post date:** [July 4, 2019, 7:14pm UTC](https://forum.sierrawireless.com/t/hl8518-921600-baudrate-and-cmux/16893/1 "2019-07-04T19:14:54Z")
I’m trying to change the baudrate of the HL8518 to the maximum value in combination with CMUX: 921600 (AT+IPR) According to the specifications, CMUX supports transmission up to 1Mbit/s (no sure why this is not 921600??) However after a few seconds the CMUX just explodes and the module start responding in non-cmux packages. Is 92600 not supported for CMUX? 230400 seems to work fine ---
**Author:** ![Sierra\_klin2](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/sierra_klin2/32/4769_2.png) [@Sierra\_klin2](https://forum.sierrawireless.com/u/Sierra_klin2)\ **Post date:** [July 5, 2019, 3:02am UTC](https://forum.sierrawireless.com/t/hl8518-921600-baudrate-and-cmux/16893/2 "2019-07-05T03:02:02Z")
Hi, 921600 is not supported by +CMUX. See below AT log and AT guide Rev19.0. ATI HL8518 OK ATI3 RHL85xx.5.14.0.7.5.20171229.x6255 OK AT+CMUX=? +CMUX: (0),(0),(1-7),(1-1509),(1-255),(0-5),(2-255), OK //AT+CMUX=,,\,,,,,, //\ 1 9 600 bit/s 2 19 200 bit/s 3 38 400 bit/s 4 57 600 bit/s 5 115 200 bit/s 6 230 400 bit/s 7 1 Mbit/s ---
**Author:** ![roel0](https://avatars.discourse-cdn.com/v4/letter/r/eb8c5e/32.png) [@roel0](https://forum.sierrawireless.com/u/roel0)\ **Post date:** [July 5, 2019, 12:06pm UTC](https://forum.sierrawireless.com/t/hl8518-921600-baudrate-and-cmux/16893/3 "2019-07-05T12:06:00Z")
And why does it support 1Mbit/s while this is not a supported baudrate, whats the purpose? ---
**Author:** ![Sierra\_klin2](https://sea1.discourse-cdn.com/flex025/user_avatar/forum.sierrawireless.com/sierra_klin2/32/4769_2.png) [@Sierra\_klin2](https://forum.sierrawireless.com/u/Sierra_klin2)\ **Post date:** [July 10, 2019, 3:30am UTC](https://forum.sierrawireless.com/t/hl8518-921600-baudrate-and-cmux/16893/4 "2019-07-10T03:30:50Z")
Hi roel0, For +CMUX, the HL8518 respects the 3GPP TS 27.007, and 921600 is not supported. Refer to [https://www.3gpp.org/ftp/Specs/archive/27\_series/27.007/](https://www.3gpp.org/ftp/Specs/archive/27_series/27.007/) (Chapter 5.7 Multiplexing mode +CMUX)