Connecting RS232 between DragonBoard and RoboRIO

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Connecting RS232 between DragonBoard and RoboRIO

Post  ljking on Wed Jan 14, 2015 3:54 pm

First lets look at the RoboRIO RS232 input. The interface has 4-pins
1) Ground
2) TxD
3) Rxd
4) +5V
We don't need the +5V signal, so lets just ignore that pin.

According to the RoboRio datasheet the RS232 port meets the following specifications:

Maximum BAud Rate 115200
Data Bits 5,6,7,8
Stop bits 1,2
Parity Odd, Even, Mark, Space
Flow Control XON/XOFF
Logic Level
Standard Meets TIA/EIA-232F voltage levels.
Receiver Input Voltage +/-30V Max
Output High voltage 5V maximum
Output Low voltage -5V maximum

This is absolutely 'standard' and shouldn't present any issues.

We have two ways to connect to the DragonBoard.The 'best' choice is to use the
three-pin connector on the DragonBoard which has GND, TxD and RxD pins and are
fully compatable with the RoboRIO. The connection would be simply 3 wires. The
'problem' with this is the three-pin port is used for log messages and for the
Linux Kernel operator console. I am discussing with the software team how to
disable log messages and the operator console so that we can use this port. I
am not 100% certain we can do this, but I am at 90% confidence it can be done.

The second choice is to use a USB to RS232 adaptor which we can get from the
usual suppliers:
I know this will work, but takes more space, weight, and cost. It also requires
a little wiring to connect to the DB9 connector to the RoboRIO. Consider this
to be the fall-back plan.


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