# FX30S serial port does not work

**URL:** https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007
**Category:** Legato Application Framework
**Created:** [March 17, 2026, 7:01pm UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007 "2026-03-17T19:01:26Z")
**Posts on this page:** 7
**Page:** 1

<div class="post-metadata">

### Author: ![TheGod](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/thegod/32/252_2.png) [@TheGod](https://forum.legato.io/u/TheGod)
#### Post date: [March 17, 2026, 7:01pm UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/1 "2026-03-17T19:01:26Z")

</div>

I was using serial port DB9 on FX30 in the past. It does not work on FX30S with firmware version 21.05.0. There is no rs\_mode file (switch between RS232 and RS485). My app is fine because everything is working when I use RS485 IoT card. I have got ttyHS0 and ttyHS1 in dev folder. ttyHS1 (IoT slot works) ttyHS0 (DB9 does not work).

 ![image](https://us1.discourse-cdn.com/flex019/uploads/legato1/original/2X/c/c325f9ba2664f01448bb0f682075efceb8408ff5.png)

 ![image](https://us1.discourse-cdn.com/flex019/uploads/legato1/original/2X/3/3d5391cc6205cbf82149f93dda287d8e1af278a7.png)

---

<div class="post-metadata">

### Author: ![jyijyi](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/jyijyi/32/822_2.png) [@jyijyi](https://forum.legato.io/u/jyijyi)
#### Post date: [March 18, 2026, 2:08am UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/2 "2026-03-18T02:08:55Z")

</div>

how about setting AT!MAPUART=14,1

 ![image](https://us1.discourse-cdn.com/flex019/uploads/legato1/original/2X/9/92f35ce0e542005e6ea9b8631f6bc6432c96e0c0.png)

---

<div class="post-metadata">

### Author: ![TheGod](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/thegod/32/252_2.png) [@TheGod](https://forum.legato.io/u/TheGod)
#### Post date: [March 18, 2026, 8:30am UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/3 "2026-03-18T08:30:39Z")

</div>

I have tried this before. When I setup service to 14, **ttyHS0** disappears.

 ![image](https://us1.discourse-cdn.com/flex019/uploads/legato1/original/2X/1/13f489a694c0e842f1e04d472f5d3cfbf16317e5.png)

---

<div class="post-metadata">

### Author: ![jyijyi](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/jyijyi/32/822_2.png) [@jyijyi](https://forum.legato.io/u/jyijyi)
#### Post date: [March 18, 2026, 8:44am UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/4 "2026-03-18T08:44:05Z")

</div>

For FX30(WP7702) FW15, if setting AT!MAPUART=14,1 for RS485 mode, it will enumerate /dev/ttyMSM0

---

<div class="post-metadata">

### Author: ![TheGod](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/thegod/32/252_2.png) [@TheGod](https://forum.legato.io/u/TheGod)
#### Post date: [March 18, 2026, 8:49am UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/5 "2026-03-18T08:49:56Z")

</div>

It is not in /dev folder

 ![image](https://us1.discourse-cdn.com/flex019/uploads/legato1/original/2X/d/d82e05c9ecfac2078388156454ea41db98363182.png)

---

<div class="post-metadata">

### Author: ![jyijyi](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/jyijyi/32/822_2.png) [@jyijyi](https://forum.legato.io/u/jyijyi)
#### Post date: [March 18, 2026, 8:59am UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/6 "2026-03-18T08:59:53Z")

</div>

I don’t see problem…

did you reset the module?

```auto
root@fx30:~# microcom /dev/ttyAT
ati8
Legato Ver: 21.05.0.54b96444_0a6e18078edde5151619cb964564694d
Yocto Ver: SWI9X06Y_03.00.13.00 2022-12-28_08:23:43
OS Ver: Linux version 4.14.253 (oe-user@oe-host) ( gcc version 9.3.0 (GCC), GNU ld (GNU Binutils) 2.34.0.20200220) #1 PREEMPT Wed Dec 28 07:40:21 UTC 2022
LK Ver: 1.3.0_1aea4d8ec8
RootFS Ver: SWI9X06Y_03.00.13.00 2022-12-28_08:23:43
UserFS Ver: unknown
MCU Ver: 002.015

OK
at!mapuart?
!MAPUART: 14,16

OK
root@fx30:~# ls /dev/ttyMS*
/dev/ttyMSM0 /dev/ttyMSM1
root@fx30:~#

```

---

<div class="post-metadata">

### Author: ![TheGod](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/thegod/32/252_2.png) [@TheGod](https://forum.legato.io/u/TheGod)
#### Post date: [March 18, 2026, 9:26am UTC](https://forum.legato.io/t/fx30s-serial-port-does-not-work/7007/7 "2026-03-18T09:26:40Z")

</div>

I did not have the same Firmware version you have got. I have downloaded and installed firmware from official website. Now, I have got /dev/ttyMSM0 and RS485 is working fine. Thanks