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TM4C1294NCPDT: EK-TM4C1294 Launchpad USB connection

Varun Rege
Prodigy 70 points
Part Number: TM4C1294NCPDT
Other Parts Discussed in Thread: EK-TM4C1294XL

Hello. I am preparing a custom design using the TM4C1294NCPDT microcontroller, for which I'm referring to the schematic and design of the EK-TM4C1294XL launchpad. I wish to add a USB port to my design for power supply and programming.

The datasheet of the TM4C1294NCPDT shows pins 93 (PL7) and 94 (PL6) as the USB0D+ and USB0D- pins, respectively. On the EK-TM4C1294XL launchpad, these pins are connected to the target USB port, which is a Micro-AB port. Meanwhile, the debug USB port which is a Micro-B port is connected to the onboard TM4C123G debugger.

 

Shown above is the debug USB port connection in the EK-TM4C1294XL launchpad schematic. But I don't see how the debugger chip communicates with the TM4C1294NCPDT microcontroller; maybe I'm missing something but I wasn't able to find a connection from the TM4C123G chip to the TM4C1294NCPDT chip in the Eagle design. Can someone point it out or explain it please? 

Meanwhile the target USB port is connected directly to the TM4C1294NCPDT pins described above, with test points on every connection. So on my custom design, if I use a Micro-AB port and connect its D+ and D- pins to pins 93 and 94 of the TM4C1294NCPDT, along with the appropriate reset and power connections, will I be able to power up and program my design over USB just like the launchpad? Or will I have to include the TM4C123G chip as well?

  • 0
    TI__Guru 72500 points

    The TM4C123 device connects to the TM4C129 device using the JTAG pins. GPIO pins PA2, PA3, PA4 and PA5 of the TM4C123 connect to JTAG pins PC0, PC1, PC3 and PC2 of the TM4C129 device. 

    Your design may be able to be powered using the USB connector depending on total power requirements. Please see the TM4C129x System Design Guidelines.

    You can program a blank device using the USB port using DFU (device firmware update) mode, but for development and debug you really need a JTAG port on your design. (The schematic snippet you gave seems to show you have included one.) You can use your EK-TM4C129XL to program your custom design as described on page 21 of the EK-TM4C1294XL User's Guide.

  • 0 in reply to Bob Crosby
    Prodigy 70 points

    Hello, Bob. Thanks for replying.

    While the schematic snippet above isn't my own custom design (it's the EK-TM4C1294 launchpad), I have indeed included a JTAG port in my design and even programmed and debugged the microcontroller with it. But what I actually wanted was to use only the USB port to program and debug my design, basically exactly like how we use the launchpad. Is that possible without an extra TM4C123G chip?

    Also, I have been wondering on how to connect the VBUS pin of the USB port on my board, as my board is powered externally with a power supply and doesn't  need the USB host supply through VBUS. I read on many sites that I shouldn't connect the VBUS pin to the power pins on my board, but I shouldn't leave it floating either. On reading the datasheet further, I think it's supposed to be connected to the USB0VBUS pin (PB1) of the TM4C1294NCPDT. Am I right or is it supposed to be configured another way?

  • 0 in reply to Varun Rege
    TI__Guru 72500 points

    Varun Rege said:
    But what I actually wanted was to use only the USB port to program and debug my design, basically exactly like how we use the launchpad. Is that possible without an extra TM4C123G chip?

    You cannot debug using only the USB port. You can program, but only using DFU on blank devices or devices where you have implemented a call to the bootloader. 

    The connection of VBUS to USBVBUS depends on the mode you will be using. See section 4.1, 4.2 and 4.3 of the TM4C129x System Design Guidelines.