# RTL8722DM(AMB21) UART3 not working

**URL:** <https://forum.amebaiot.com/t/rtl8722dm-amb21-uart3-not-working/1348>\
**Category:** Peripherals\
**Tags:** uart, rtl872xd\
**Created:** [July 14, 2022, 9:42am UTC](https://forum.amebaiot.com/t/rtl8722dm-amb21-uart3-not-working/1348 "2022-07-14T09:42:05Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Po\_Quan\_Hsieh](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.amebaiot.com/po_quan_hsieh/32/1065_2.png) [@Po\_Quan\_Hsieh](https://forum.amebaiot.com/u/Po_Quan_Hsieh)\
**Post date:** [July 14, 2022, 9:42am UTC](https://forum.amebaiot.com/t/rtl8722dm-amb21-uart3-not-working/1348/1 "2022-07-14T09:42:05Z")

</div>

Hi,  
I started development with Standard SDK([which is downloaded GitHub](https://github.com/ambiot/ambd_sdk/releases/tag/QC-V1.0.0)) on AMB21 evaluation board.  
I referenced the uart\_stream\_data example(example\_sources\UART\mbed\uart\_stream\_dma) and add in the main.c and it works.  
Then I tried to use UART0 and UART3 with PA25 and PA26(which are defined in the serial\_api.c), but it didn’t work. What might be the reason?  
By the way, which repository is the most recommaneded? [The newest repository](https://github.com/ambiot/ambd_sdk) or [the QC-V1.0.0](https://github.com/ambiot/ambd_sdk/releases/tag/QC-V1.0.0) or [Realteck website](https://www.amebaiot.com/zh/ameba-sdk-summary/)?

---

<div class="post-metadata">

**Author:** ![wyy](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wyy](https://forum.amebaiot.com/u/wyy)\
**Post date:** [July 15, 2022, 3:20am UTC](https://forum.amebaiot.com/t/rtl8722dm-amb21-uart3-not-working/1348/2 "2022-07-15T03:20:13Z")

</div>

Hi @Po_Quan_Hsieh

UART 3 does not have a DMA interface, thus the uart\_stream\_dma example will not work with this UART. If you wish to use UART 3, you should use the non-DMA examples.

It is recommended that you use the [Release V1.0.0](https://github.com/ambiot/ambd_sdk/releases/tag/QC-V1.0.0) version.

---

<div class="post-metadata">

**Author:** ![Po\_Quan\_Hsieh](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.amebaiot.com/po_quan_hsieh/32/1065_2.png) [@Po\_Quan\_Hsieh](https://forum.amebaiot.com/u/Po_Quan_Hsieh)\
**Post date:** [July 15, 2022, 6:57am UTC](https://forum.amebaiot.com/t/rtl8722dm-amb21-uart3-not-working/1348/3 "2022-07-15T06:57:02Z")

</div>

Hi @wyy ,  
Thanks for your help, after applying uart\_stream\_irq example into the main.c, the UART0 DMA and UART3 IRQ both work fine.