LPC1788: USB D+ Line pull-down after 11us

[paul_shaffer]

I would like more information about theUSB 2.0  D-PLUS line on the NXP part number LPC1788 microcontroller. When we power up, the D+ line starts to go "tri-state", then after 11us, the D+ line is internally pull-down to ground.  Why?

[Sabina_Bruce]

Hi Paul,

In the LPC1788 the USB D+ is initially a GPIO pin, which after a reset is configured as an input. This will cause it to be at a high impedance. Once the usb is configured and the internal pull down is enabled you will see the change in state. However this behavior from its power on state to once the pins are configured should not impact your project.

If you have any further questions please dont hesitate to ask.

Hope this helps and have a great day!

Sabina