[Arm-netbook] [EOMA68] RS232 on SoCs

[Vladimir Pantelic]

On 09/03/2013 10:21 AM, joem wrote:
> On Tue, 2013-09-03 at 09:10 +0200, Vladimir Pantelic wrote:
>> On 08/31/2013 04:59 PM, Henrik Nordström wrote:
>>
>>>
>>> It's not about excessive current. It's about powering the chip via I/O
>>> pins instead of power pins. Now the Allwinner chips do not really power
>>> up via the I/O pins, but there is at least sufficient power leakage back
>>> to the power rails to cause problems for the AXP power management
>>> controller chip, and maybe some internal I/O functions as well.
>>
>> and a 1k series resistor on the UART line is not enough to stop this?
>
> No - as soon as you exceed 3.3V, the IO line's protection diodes start
> conducting and you will end up powering the CPU through the power line
> from the UART and the chip can no longer function properly.

well yes, I assumed one would use a 3.3V serial converter on a 3.3V 
device...