Can you access UART2 when SimpleRTK2B XBee socket is switched to UART1

Q&A forumCategory: QuestionsCan you access UART2 when SimpleRTK2B XBee socket is switched to UART1
AndrewRL asked 7 months ago
The hookup guide says for the Arduino rails

  • TX2: XBee UART TX (this pin is also connected to ZED-F9P UART2 RX).
  • RX2: XBee UART RX (this pin is also connected to ZED-F9P UART2 TX).

Which is it? Are these pins connected to UART2 or are they connected to the XBee socket?
On the v3 board I had assumed that TX2 and RX2 were hardwired to UART2 and that the switch under the XBee socket merely controlled which UART the XBee was connected to.
I was disappointed to discover that the switch also controlled which UART RX2 and TX2 were connected to so that if it was switched to UART1 then TX2/RX2 were likewise connected to UART1 and UART2 was not accessible at all.
I am now thinking of ordering a v4/Pro board. Does it work the same way, or is UART2 now available on the rails when the XBee socket is switched to UART1? 

1 Answers
Ardusimple Staff answered 7 months ago
Dear Andrew,
You can only either / or. You can’t have access at the same time to the XBee UART and to the UART2 of the GPS. WIth the PRO boards is the same limitation.
Unfortunately the Pro board’s switch is for basic users who simply want to use UART1 on the XBee socket and nothing else.
replied 7 months ago

Thank you for the explanation, but you risk devaluing your own product – I assumed “Pro” indicated “Professional” not basic 🙂

At the time I was in a rush, canibalising boards to make do when the original SimpleRTK2B died, but it had seemed a nice idea to have both Bluetooth (Xbee) and USB issuing the same full bodied less frequent feed, with UART2 feeding a slimmed down GGA/VTG @ 10Hz hardwired to a mini TTL-RS232 board to suit agric machinery.

To do this should I have used a “Shield for second Plugin Socket”, with the main board set to UART2 (to stop both XBees being connected to UART1)?

I assume the switch on that shield merely swaps the tracks to the XBee between RX1/TX1 on the rails and RX2/TX2 on the rails?

Would it make sense for v5 (?) of SimpleRTK2B to work the same way – ie hardwire the rails to UART1 and UART2 and merely switch the Xbee between one and the other so that you never lose access to a UART?

Or are there existing use cases which would not appreciate that (if so perhaps UART2 could appear on some currently spare pins)?

Meanwhile perhaps an amendment to the hookup guides to clarify that RX2/TX2 are NOT connected to UART2, merely to whichever UART the XBee happens to be switched to for the time being?

replied 6 months ago

I guess some of this stems from a desire to keep-it-simple and not use an MCU on the board, or load it up with switching logic and diodes, etc.

The resources are relatively finite, the choice of MCU will cause all kinds of religious wars..

If you can use an Arduino, RPi, AdaFruit Grand Central, RPi PICO, or whatever, you can probably take a UART or USB feed, and then demux the data content from there into simpler / condensed forms.

The UART2 vs UART1 thing has probably changed since u-Blox now permits UBX data on UART2, whereas at release it was primarily expected to do RTCM3 input/output work for the radio link.

I’ve moved to using RPi Pico boards over USB-to-CMOS Serial adapters, as it can fill those roles, and other more complex tasks.

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