# SW7990

![Photo courtesy of xlbook on https://whycan.com/t_10014.html](https://storage.yandexcloud.net/bksp-wiki-assets/uploads/298a2e26-87de-4753-a045-717271c8b2f5/bf3de230-6df7-45f4-b1c7-338794ada405/1.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=YCAJEMO2-DwUmfLoAY9UdwOXD%2F20260911%2Fru-central1-a%2Fs3%2Faws4_request&X-Amz-Date=20260911T130000Z&X-Amz-Expires=86400&X-Amz-Signature=3b2908df2b99b109efbab8946eb1f6d6f0dc7c9cd5149df2908fa1843595607d&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject " =1920x1440")

## Flashing

Same procedure as for [King3399](/doc/rongpin-king3399-Z5A2yXNThf), but there is a microUSB port instead of USB-C, and USB boot button is next to it.

Ophub’s board name is sw799.

## Debug port

Connector labeled “Debug” is a UART2 (ttyS2).

## UART4

UART4 is populated on the small Molex PicoLock connector at the edge of the board.

However, it’s tricky to use due to:


1. It’s disabled in Device Tree in Ophub’s Armbian.
2. It’s connected via TXB0102 level shifter. Low side is 1.8V connected to RK3399, but high side VCC you should supply by yourself via one of the connector’s pins.

### Patching DT to enable UART4


:::tip
Note that during `armbian-update` you may receive an updated DTB, so keep looking for the changes, and re-patch when necessary.

:::


1. Decompile the existing DTB overlay for this board. It’s located in `/boot/dts`
2. Find the `serial4` declaration in the decompiled DTS.
3. Change its "status” from `disabled` to `okay`
4. Compile a patched DTS into DTB. *There will be a lot of warnings – it’s safe to ignore them.*
5. Replace original DTB with a recompiled one.

## Schematics


:::tip
This schematic is not for this board. But it’s first page contains a correct pin layout of a CPU mezzanine board, which is quite useful.

:::

[Fine3399_Schematic.pdf 953111](https://storage.yandexcloud.net/bksp-wiki-assets/uploads/298a2e26-87de-4753-a045-717271c8b2f5/d53f1130-5368-464f-881e-cf040ded0a16/Fine3399_Schematic.pdf?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=YCAJEMO2-DwUmfLoAY9UdwOXD%2F20260911%2Fru-central1-a%2Fs3%2Faws4_request&X-Amz-Date=20260911T130000Z&X-Amz-Expires=86400&X-Amz-Signature=151c113b311828fc90bf9732748a659c07d4de724a280b7576f30e865879cec6&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)

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**Documents**

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