Voltage on VCC pin in the UART connector drops after power on.

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akschu
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Voltage on VCC pin in the UART connector drops after power on.

Unread post by akschu » Tue Jan 28, 2020 10:09 am

I didn't get the UART/usb adapter because my vendor was out of stock, and because I have several usb to TTL uart chips in my lab.

Once I got to hooking it up, I realized that the HC2 is 1.8v TTL. No big deal I have a number of these level shifters floating around:

https://www.pololu.com/product/2595

The problem is that when I went to probe out the UART on the HC I discovered that the VCC pin goes to 1.8v on power on, but after a second, it drops back to 0v.

Once the VCC pin drops to zero, my level shifter doesn't work. Is this by design? Why wouldn't a standard level shifter work?

schu

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Re: Voltage on VCC pin in the UART connector drops after power on.

Unread post by odroid » Tue Jan 28, 2020 1:50 pm

That 1.8V output must be always enabled.
Which OS image and Kernel version do you use?

akschu
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Re: Voltage on VCC pin in the UART connector drops after power on.

Unread post by akschu » Wed Jan 29, 2020 1:29 am

I installed ubuntu image from the odroid wiki, and I do see a constant 1.662 volts now.

Does the kernel need to enable this pin? If so, then as long as the kernel is started, I should be able to see any issues in the console.

Thanks,
schu

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Re: Voltage on VCC pin in the UART connector drops after power on.

Unread post by odroid » Wed Jan 29, 2020 10:11 am

It should be enabled by u-boot and your custom kernel might disable it.
The voltage output could be controlled by the PMIC device driver.

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