I wonder if the TWR-SER module can be used as SELF-powered USB Device. In the datasheet I see jumper settings for USB host mode and for bus-powered USB device only, but not for self-powered USB device.
Yes, the TWR-SER is prepared for this. look at the schematic:
There are many ways to detect if the VBUS line has 5v. One us using the MAX3353 using I2C to check for changes on the USB VBUS line. some tower boards already have a direct connection from the VBUS line to a GPIO to detect VBUS changes directly (again depends on what MCU board you are using)
Also, all our USB parts have the D+ pull-up internally and you can enable/disable it inside the code. so once you detect the VBUS line you can take your time inside the code to do something and after that you enable the pull-up resistor and the HOST (or HUB) will start the enumeration process.
hope this help
what exactly you mean by Self-powered? you want to connect an external power supply directly on the TWR-SER instead of using the primary elevator board?
If you only don't want to use the 5v comming from the USB VBUS line you can only remove all jumpers on J16 header (TWR-SER) and the 5v VBUS will be not used at all. just keep in mind that the USB modules needs 3.3v on the Vout33 pin to operate so you must have a valid voltage on VregIN pin.
all our tower boards have a jumper to connect a 5v reference to the VregIN pin but it is different on each MCU tower board.
if you have problems finding the appropiate configuration tell us and we will be able to help you..
I wonder if the following has been implemented properly and how I have to configure TWR-SER to make sure it works properly as described (see quote below) in http://uk.farnell.com/images/en/ede/pdf/usb_dev_mistake.pdf:
Back-power: “Self-powered” USB devices can also have their own power problems. Since self-powered devices have their own independent power supplies, they can be ON while the host is turned OFF. This causes a potential problem where the small pull-up voltage applied to D+ to enable USB device detection slowly charges up the entire host system and interferes with startup. Self-powered USB devices (including battery-powered devices) must either drive this pull-up directly from VBUS or turn it off via software control using a VBUS sensor.
Thank you very much!
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