LPC MicrocontrollersのトピックRe: Is VBUS input required for device mode? https://community.nxp.com/t5/LPC-Microcontrollers/Is-VBUS-input-required-for-device-mode/m-p/523449#M6085 <HTML><HEAD></HEAD><BODY><STRONG>Content originally posted in LPCWare by Tsuneo on Tue Jul 16 03:09:52 MST 2013</STRONG><BR /><HR /><SPAN style="color: #0000ff;"><STRONG>Quote: </STRONG><BR />User Manual indicates that USB_VBUS is internally pulled high when pin is not assigned to that function. Does this just mean that the USB device system will always think that the device is connected?</SPAN><HR /><BR /><SPAN>Yes.</SPAN><BR /><SPAN>It's fine for bus-powered devices, because the running firmware means that the bus power is supplied. There is no need to detect VBUS voltage explicitly at the USB connector.</SPAN><BR /><BR /><SPAN>For self-powered devices, however, VBUS detection is necessary. Just while VBUS voltage presents, D+ pull-up resistor (ie. USB_CONNECT) is enabled, as the requirement of USB2.0 spec (*1). Also VBUS detection is required to suppress spurious USB interrupts by floating D+/D- lines.</SPAN><BR /><BR /><BR /><SPAN>(*1) </SPAN><I><STRONG>7.1.5.1 Low-/Full-speed Device Speed Identification (on usb_20.pdf)</STRONG><BR />The voltage source on the pull-up resistor must be derived from or controlled by the power supplied on the USB cable such that when VBUS is removed, the pull-up resistor does not supply current on the data line to which it is attached.</I><BR /><BR /><SPAN>Tsuneo</SPAN></BODY></HTML> Wed, 15 Jun 2016 16:43:24 GMT lpcware 2016-06-15T16:43:24Z Is VBUS input required for device mode? https://community.nxp.com/t5/LPC-Microcontrollers/Is-VBUS-input-required-for-device-mode/m-p/523448#M6084 <HTML><HEAD></HEAD><BODY><STRONG>Content originally posted in LPCWare by jdupre on Mon Jul 15 10:20:28 MST 2013</STRONG><BR /><SPAN>I have a LPC17xx system with USB2 configured as host.&nbsp; I'd like USB1 to be in device mode.&nbsp; Unfortunately, USB_PWRD2 and USB_VBUS are on the same pin.</SPAN><BR /><BR /><SPAN>User Manual indicates that USB_VBUS is internally pulled high when pin is not assigned to that function.&nbsp; Does this just mean that the USB device system will always think that the device is connected?</SPAN><BR /><BR /><SPAN>In my case, the USB device port will either be connected to a power supply, or to a computer.&nbsp; (i.e the system gets power from the USB device port in all cases-- there is no other power supply.)&nbsp; Do I really need to detect VBUS for USB device mode to work?</SPAN></BODY></HTML> Wed, 15 Jun 2016 16:43:23 GMT https://community.nxp.com/t5/LPC-Microcontrollers/Is-VBUS-input-required-for-device-mode/m-p/523448#M6084 lpcware 2016-06-15T16:43:23Z Re: Is VBUS input required for device mode? https://community.nxp.com/t5/LPC-Microcontrollers/Is-VBUS-input-required-for-device-mode/m-p/523449#M6085 <HTML><HEAD></HEAD><BODY><STRONG>Content originally posted in LPCWare by Tsuneo on Tue Jul 16 03:09:52 MST 2013</STRONG><BR /><HR /><SPAN style="color: #0000ff;"><STRONG>Quote: </STRONG><BR />User Manual indicates that USB_VBUS is internally pulled high when pin is not assigned to that function. Does this just mean that the USB device system will always think that the device is connected?</SPAN><HR /><BR /><SPAN>Yes.</SPAN><BR /><SPAN>It's fine for bus-powered devices, because the running firmware means that the bus power is supplied. There is no need to detect VBUS voltage explicitly at the USB connector.</SPAN><BR /><BR /><SPAN>For self-powered devices, however, VBUS detection is necessary. Just while VBUS voltage presents, D+ pull-up resistor (ie. USB_CONNECT) is enabled, as the requirement of USB2.0 spec (*1). Also VBUS detection is required to suppress spurious USB interrupts by floating D+/D- lines.</SPAN><BR /><BR /><BR /><SPAN>(*1) </SPAN><I><STRONG>7.1.5.1 Low-/Full-speed Device Speed Identification (on usb_20.pdf)</STRONG><BR />The voltage source on the pull-up resistor must be derived from or controlled by the power supplied on the USB cable such that when VBUS is removed, the pull-up resistor does not supply current on the data line to which it is attached.</I><BR /><BR /><SPAN>Tsuneo</SPAN></BODY></HTML> Wed, 15 Jun 2016 16:43:24 GMT https://community.nxp.com/t5/LPC-Microcontrollers/Is-VBUS-input-required-for-device-mode/m-p/523449#M6085 lpcware 2016-06-15T16:43:24Z