UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

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tedzini
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UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

Unread post by tedzini » Sat Oct 19, 2019 1:33 am

We followed N2 wiki to enable UART A/B TTL. Used
one of the ODROID cables to test and everything fine. But then I tried RS232/TTL converter.
There is a 3.3-5V line which I plugged into P38. After never getting that device to work, I
rebooted but then the HDMI HD monitor indicated it could not sync to 1920x1024 60Hz.
In addition I could no longer connect to ssh. Then I recycled power (the red light and blue lights
were flashing in either case), and at least I was able to ssh in..

My question is are the UART I/O lines actually 1.8V and NOT 3.3V? The reason I ask is because
the documented Ext 40p diagram for the N2 indicate #38 as 1.8 and not 3.3V. I
tried the 3.3 volt line and with no luck. I think I partially fried my N2. :-(

Any help would be greatly appreciated. If it can only handle 1.8V any suggestions for TTL/DB9 RS232
device known to work with the N2 would be greatly appreciated.

Thanks anyone!

-t

tedzini
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Re: UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

Unread post by tedzini » Sat Oct 19, 2019 1:51 am

To reply to my own post, has anyone tried:

https://www.amazon.com/Ultra-Compact-RS ... B074BTGLJN

which they *advertise* as handling 1.8V levels directly.

Or, the other option I was looking at involves shift/logic converter. That way I could used the devices
we already have (in theory?):

https://www.eevblog.com/forum/beginners ... ver-where/


-t

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Re: UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

Unread post by tobetter » Sat Oct 19, 2019 3:10 am

All GPIO level on the pin header is 3.3V, I am afraid of your board defective.

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Re: UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

Unread post by rooted » Mon Oct 21, 2019 10:34 pm

tobetter wrote:All GPIO level on the pin header is 3.3V, I am afraid of your board defective.
You mean damaged?

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Re: UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

Unread post by tobetter » Mon Oct 21, 2019 10:47 pm

rooted wrote:
Mon Oct 21, 2019 10:34 pm
tobetter wrote:All GPIO level on the pin header is 3.3V, I am afraid of your board defective.
You mean damaged?
Yes, I suspect N2 is damaged through P38.
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rooted (Mon Oct 21, 2019 10:49 pm)

tedzini
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Re: UARTA (ttyS1)/UARTB (ttyS2) voltage levels?

Unread post by tedzini » Tue Oct 22, 2019 4:14 am

I see. Perhaps I'll check the voltage level now of P38. I suppose I can also do the test published on
the WIKI.

thanks,
-ted

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