On 04/16/2013 09:26 PM, Robert Moskowitz wrote:
On 04/16/2013 08:58 PM, Scott Sullivan wrote:
You'll find the vast majority of arm devices do not have proper 12v
RS232. Instead they have a UART which is serial with only the TX, RX
and GND lines. The usually operate at the core logic voltage of the
SoC and if you apply the wrong voltage you'll fry the UART.
Yet there are the USB to serial devices that work off the 5v USB just
fine. Or fine enough to connect to a serial port on a firewall, switch
or router.
The serial adapter you linked to is a 'proper'* 12V RS232 adapter. What
it's doing is converting the 5V from the USB power up to the 12V need
for the serial. The USB adapter I have for the pogoplug down converts to
3.3V which is what the UART on the PogoPlug.
Serial signaling is done using voltage changes to indicate logical 1 or
0. http://en.wikipedia.org/wiki/RS-232#Voltage_levels
If you try to use a serial adapter that is the wrong voltage you get
problems ranging from 'doesn't work' becasue the voltage is to low to
register as logical HIGH, all the way to 'doesn't work' because you
applied more voltage then the UART is designed to tolerate.
If I plug mine in to the USB, will it be recognized during the boot? Or
does it need Linux running, so it can't be used as a boot monitor?
Ah! I get you, your hoping the PogoPlug will see the USB adapter during
boot and auto-configure it as it's console and talk to you. No dice. No
one builds a distro with that much smarts. The serial all the tutorials
are refering to is the UART inside the case where the linux and uboot
consoles are configured to talk on.
Most of my devices have had 3.3v serial UARTs including the openWRT
capable routers I experiment with, so I invested in that adapter. It's
served me rather well as I can easily us jumper wires for custom
adapter cables for each board.
So to do this, I am going to have to invest in some hardware. :(
To use the serial UART console on the pogoplug, yes. But the
instructions on the wiki we're made with the goal that you should not
have to use the serial console.
I've got a USB stick being prepared right now and I've already gone
through the uboot upgrade on one of the few virgin model Pogo-E02 's I have.
I'll post my notes when I'm done.
--
Scott Sullivan
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