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MKL27Z256 USB connection

Question asked by Joey Gouly on Sep 20, 2015
Latest reply on Sep 21, 2015 by Joey Gouly

Hi all,

 

I designed and made a PCB based on the MKL27Z256, unfortunately I'm having trouble with USB.

I think there might be something wrong with the USB connection, since when I plug it in it, the ROM bootloader should start, doesn't show up in dmesg as a USB device.

I have the ROM bootloader working with LPUART, but I want to get it working with USB to make sure that the USB connection is functional before trying to get my own USB stack working.

 

Note: I actually designed this for a MKL26Z256 part, but changed it at the last moment, but I think the USB parts are identical between the two.

 

Schematic:

4A2BZae.png

PCB routing part:

6jlsSYl.png

I picked a "bad" usb connector that meant I had to swap the DM & DP pins with a via.. but since the traces are quite short I hoped it wouldn't be an issue. On the next revision, I'm definitely going to fix that.

 

I have tried testing the USB data lines with a multimeter and things seem ok. VBUS is also working, since I'm using it to power the board.

 

I'm just looking for some help on what might be wrong, and why the ROM bootloader wouldn't start over USB. I'm not actually sure *if* I should be seeing something in dmesg on Linux (I also have a Windows machine I can try, but not sure what I should see there either)

 

Any help appreciated!

 

Joey

ps. I have a couple of assembled boards, so might try the others, to see if this is just a bad one.

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