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Nick
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| Pic18f2550 using USB questions |
 Posted: Fri Nov 11, 2005 1:30 pm |
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I’m reading the datasheet and I have some questions and I would also like verification on the parts that I believe I understand
USB Purpose: to transfer the pic’s eeprom data to and from a computer, but speed is not a requirement. also do bootloader updates
Question 1: most people will be using older equipment that I assume they have the older usb specification. If I use full speed usb configuration will the older laptop’s usb ports not work?
Question 2: On the pinout description in the datasheet when it says ‘ra0/an0’ I assume that I can do digital I/O on that pin since it has both labels. Is this correct?
Question 3: I would like to create a demo board using the 20mhz cr I use for my pic16f876, but I am not sure they will work. In the datasheet under the oscillator configuration options it shows input oscillator 20mhz then says ppl division %5 and some other data. My question dumbed down is can I use the 20mhz cr for the microcontroller and still use its built in usb module? |
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Darren Rook
Joined: 06 Sep 2003
Posts: 287
Location: Milwaukee, WI
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| Re: Pic18f2550 using USB questions |
| Posted: Sat Nov 12, 2005 1:59 pm |
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| Nick wrote: |
Question 1: most people will be using older equipment that I assume they have the older usb specification. If I use full speed usb configuration will the older laptop’s usb ports not work? |
I have never seen this problem. In fact, I wouldn't be surprised that USB 1.0+ *certified* Host Controllers must at least have Full Speed mode.
| Quote: | | Question 2: On the pinout description in the datasheet when it says ‘ra0/an0’ I assume that I can do digital I/O on that pin since it has both labels. Is this correct? |
Yes.
| Quote: | | Question 3: I would like to create a demo board using the 20mhz cr I use for my pic16f876, but I am not sure they will work. In the datasheet under the oscillator configuration options it shows input oscillator 20mhz then says ppl division %5 and some other data. My question dumbed down is can I use the 20mhz cr for the microcontroller and still use its built in usb module? |
Any oscillator will work as long as it's evenly divideable by 4MHz, so yes a 20Mhz oscillator will work.
The biggest gotcha for someone using the 18Fxx5x family for the first time in USB is that RC3 has been removed and replaced with Vusb, and that this pin needs a 200 to 500nF capacitor to help out the internal USB regulator. |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Re: Pic18f2550 using USB questions |
| Posted: Sat Nov 12, 2005 6:29 pm |
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| Darren Rook wrote: | | Nick wrote: |
Question 1: most people will be using older equipment that I assume they have the older usb specification. If I use full speed usb configuration will the older laptop’s usb ports not work? |
I have never seen this problem. In fact, I wouldn't be surprised that USB 1.0+ *certified* Host Controllers must at least have Full Speed mode.
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I have seen this problem with a USB 1.0 implementation however I would not worry about it because the number of USB 1.0 devices "in the wild" is not high enough to worry about.
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Nick
Guest
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| Posted: Sun Nov 13, 2005 12:39 pm |
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| thanks guys |
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