Interfacing Xbee with Nexys4 Artix7 FPGAboard

[Manas]

Hi,

I have read the possibilities of Xbee and used it using arduino Uno board. Now, I facing problem on how to interface this on Nexys 4 Artix 7 FPGA Board. Basically i'm confuse on how to proceed on FPGA board. I have already started looking on UART protocol and its implementation. Please help me out on how to proceed forward.

With regards

Manas

 

[D@n]

@Manas,

You didn't specify which XBee you were interested in, so I took a guess and looked into the XBee WiFi specification.  I tried really hard to find a clear statement of the voltage standard that the XBee was looking for, but the closest I found was the electrical specification for the GPIO pads on p15 which suggested a 3.3V I/O standard.  If so, the task becomes one of wiring the two devices together.

Your board has a variety of PMod connectors on it.  You'll want to wire one of these module connectors to the XBee.  How you wire it is somewhat dependent on which of the two XBee protocols you use: UART or SPI.  Since you mentioned UART above, I'd recommend you look at the pin out of the PModUSBUART (found here) and use those pins to line up with the XBee board pins.  That way, if you wanted to, you could swap devices (XBee and PModUSBUART) and debug any problems using the PModUSBUART and your host PC before going back to the XBee.

As for how to work with a UART, I put together a UART demo project that you can use, having some simple read/write UART verilog code showing how to set up and interact with a UART.

Let us know if you have more questions.

Dan

[Manas]

Hi D@n,

Thanks for help. I only intend to do point to point communication using the either series 1 0r 2 XBEE. I was contemplating on using the usb-uart onboard the Nexys4 Artix 7 FPGA board. Even if i go wiith the PModUSBUART, i still have confusion on how the connection should be done with the FPGA board. Do we make use of an general FTDI cable available? Yes, the Xbee operates on 3.3V, so I was contemplating on using the PMod connectors since it give 3.3V output. Is it necessary  to use PModUSBUART. I still have difficulty in visualising how connection should be done. Kindly look into this.

With Regards

Manas

[Manas]

Hi
 

I'm not clear on how to connect the suggested PModUSBUART with the Xbee. Since I don't have the PMOdUSBUART, i was thinking to the on board usb-uart via FTDI adapter to connect with the Xbee. For power the FPGA board i plan to use the power jack. Kindly look into this.

With regards

Manas

 

[D@n]

@Manas,

I think you misunderstood me.

The Nexys board you are referencing has a USB-UART/JTAG bridge.  This is your primary means of communicating with the board, both for downloading bitfiles and returning status as to how well the board is or is not working.  It does not contain a PMod USBUART, which is an external PMod device that would connect to one of the PMod ports--such as the one you would need to wire up in order to connect your XBee to the Nexys.  I would not recommend soldering wires to the FTDI-Xilinx traces in order to connect them to your XBee board.  That means that whatever you do will need to go through the FPGA.  Connecting to a PMod at that point makes the most sense, and requires the least electrical wizardry.

UART communication requires two wires (transmit and receive) and a common 3.3V power and ground.  That's it.  You can also add the two more wires (RTS/CTS) for hardware handshaking.  The one handshaking wire from your XBee can be ignored, and the one to the XBee can be set to a constant--just to get things going.  Still, these are the four connections the XBee requires.

Every 6-pin PMod row contains four data pins, power, and ground.  You'll want to connect these four data pins to your XBee to do UART with your XBee.  You do not need an FTDI adaptor, and I doubt you'll find a premade cable that does the job--although I might recommend a PMod cable set to you.  Be prepared to get your hands dirty while wiring up your XBee.  You will also need to create a configuration within your Nexys that sets up the wires to the Pmod you are using and communicates properly with them.  You might wish to make your initial program a simple pass through, logically connecting the wires from the FTDI to the Pmod--that'd allow you to access the XBee from your PC/Host computer to both know that it works and to experiment with some commands ... without worrying about whether or not you had all your logic set up properly within the Nexys.  (That'd be the next step)

Should you choose a means of connecting these four pins that is pin compatible with a PMod USBUART (not required), then you will then be able to swap the XBee for the PModUSBUART and debug what is going on.  You can use the pinout from the PModUSBUART reference should you wish to duplicate this interface, but in reality your choice of wiring is completely arbitrary.
Dan