I am adapting a design using a PIC32MX (which is actually working) to put an extra add-on. The add-on is a fingerprint reader which communicates via UART. Regarding that I have the USB pins exposed in my design, I found a way to connect a ftdi 3.3V (https://www.sparkfun.com/products/9716) between UART and USB.
I am planning to connect my VCC ( 3.3V in my design , which I believe it can give me more than 200 mA) to the VUSB red wire cable. The other pins are straight forward.
So my questions from now are:
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The purpose of the VBUS pin on the PIC32mx is to recognize if there's any device plugged or not, right? Is there any problem if I leave it not connected?
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Do I need to connect the VBUSON pin to somewhere? I am already using for something else (the pin is shared/not dedicated).
Best Answer
Q1: No. The VBUS pin is used when your PIC32MX is itself acting as a device and it tells the PIC32's USB module when it has been connected to a USB host (like a PC) by detecting the nominal 5V which should be present.
Q2: As the manual tells us, the VBUSON pin is "USB Host and OTG bus power control output". In other words, this pin turns the Vbus 5V output from your board on/off when your PIC32 is acting as a USB host.
To address a question which you haven't asked ... your PIC32 must be operating as a USB host in order for your FTDI USB UART to be of any use. This means that it must be configured correctly and running a USB host firmware stack.