Edited by kordian at 2016-2-13 07:28

Hi!
I'm trying to communicate OPI Plus2 with Arduino, so I need working UART. I'm using Jacer's Debian Jessie ( LINK ).
I've converted good-working script.bin (Plus 1080p60 HDMI) to fex file, and enabled serial ports (for all ports I've changed to uart_used = 1 and uart_type = 2, without touching anything else).
Before this, I had three available serial ports:
Now, I have one additional port (/dev/ttyS1), what allows me to suppose that everything went okay (because in previous FEX version UART2 was disabled).
Although I can open these ports in minicom or python program, only /dev/ttyS0 is working (three-pin debug connector).
I've tried CON3 pins (8, 10) for /dev/ttyS2 and (11, 13) for /dev/ttyS1, but I'm not able to send nor receive anything. Additionally, the board is very unstable, when something is connected to pins 11 and 13 (especially when booting).

What can I do to make UART3 working?

Thank you!

If you're using 5V Arduino, then you might need to buy logic level converter (or make a resistor divider for RX pin), because H3 UART (UART RX in your case) isn't 5V tolerant. This can burn your board or make it unstable.

Edited by kordian at 2016-2-13 06:46

Thank you for your reply! I'm using 3.3V one, but it is really important to remember about voltage levels.

After checking everything once again, I found my mistake. Pins 8 and 10 are assigned to /dev/ttyS3, not /dev/ttyS2. So, right now I've got one working serial port and one serial console (on three-pin header), so I can use it in my project.

Although I've resolved my problem, I'm really curious if is it possible to make UART2 /dev/ttyS2 (pins 11 and 13) or UART1 /dev/ttyS1 (pins 38 and 40) working, or is it impossible?
These ports are not working, even if shorted RxD with TxD (simple loopback).

Kindest regards,
K.