xDot Developer's Kit External Power/UART

[Bryce Himebaugh]

I have been using my xDot Developer’s Kit through the USB interface. All works well in this mode. I am trying to connect the board to an external microcontroller based on the notes related to setting JP5 and JP30 in the User’s Guide.

I removed JP30 (to disconnect the xDot module from the internal regulator) and added JP5 (to disable all of the buffers on the board). I am powering the board through Pin 2 of JP30 (3V), and P2 of the header pads. After trying to get things working by connecting to the UART pins (P10 and P11), it seems that the xDot reset line is floating at 1V.

I tried pulling it up with a 1K resistor with no success. I am suspicious that the MK40 mbed microcontroller might be be causing the issue in with JP5 removed and not power applied through the USB port.

Has anyone had any success in using the xDot Developer’s Kit board from an external supply?

Thanks,

Bryce

[Alejandro Gordillo]

I tired also to power the xDot from Pin2 of JP30 but had no luck. Were you able to overcome this issue?

[Leon Lindenfelser]

Hi Alejandro,

Powering the xDot without providing power on the USB connector will not work. The MK20 interface chip needs to be powered through the USB connector so it drives the NRESET line high.

The intention of JP30 and JP5 is to provide a means to measure the xDot power draw.

We will submit a request to our technical writers to correct the developer guide.

Kind regards,
Leon

[Cora Dias]

Hi…i am a new user here. I am also facing some sort of issue. If I would like to power the xdot using an external power pack (3.3V)? where should I connect the positive and the negative wire to ?

[Leon Lindenfelser]

Hi Cora,

Assuming you want to only power the xDot with your power pack, remove JP30 and connect your positive wire to the pin closest to the label JP30 and connect your ground wire to the pin closest to the label JP5 or the via (not the pin) on the other side of JP5 labeled GND.

You will also need to provide 5v into the USB connector so the interface chip is powered and providing NRESET to the xDot.

FYI, Page 51 of the developer guide contains the xDot developer board schematics.
https://www.multitech.com/documents/publications/manuals/s000645.pdf
If you want access to the command or debug serial ports without the interface chip(U6 on page 3), pay close attention to the buffers on the upper left quadrant of page 2. If those buffers are enabled, UART_RX_X/UART_TX_X and MBED_RX_X/MBED_TX_X are driven by the buffers. The UART_RX_X/UART_TX_X pins are brought out but MBED_RX_X/MBED_TX_X are not.

Kind regards,
Leon

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