[SOLVED] correct fuse settings for 18F4550 as an USB device

[varunme]

so , that too isnt the problem for my board to work ? ,
I am using 20Mhz crystal with 20Mhz firmware from microchip.
But the CPUDIV : /5 is not available in microburn fuse setting , refer my earlier post , I am too confused
PLL /5 is available

 

[betwixt]

PLLDIV and CPUDIV are different things.

PLLDIV is a programmable divider that MUST be used to set the USB speed and can optionally be used to set the CPU speed.
CPUDIV is a programmable divider that only sets the core CPU clock speed and other (non USB) peripheral speeds.

Please forget the fuse settings in microburn, under normal circumstances you never have to change them, they are set automatically by the __CONFIG directive in the source code and embedded in the HEX file. Microburn is not a clever program, it will simply use the fuse settings it sees in the HEX file, regardless of what the fuse settings screen tells you. Please remember that the last official version of microburn was released at about the same date the 18F4550 came on the market so it is quite possible that it was never tested with that PIC and some options were left out off the screen, they are still there though and will work properly.

You have never shown us your schematic, if it doesn't work I suspect your problem lies somewhere else. Can you tell us exactly what happens after you have programmed the PIC and you try to run the program.

Brian.

 

[varunme]

Can you tell us exactly what happens after you have programmed the PIC and you try to run the program.
Brian.

means ?
when i connect the pic to usb with the interfacing board , it says device not recognized
..............................................................................................................................
I am using this commercial board
**broken link removed**
ok , i will compile my own hex with their source code

in the board the reset button and the bootloader button are not connected though , its delimited by headers and option for connecting

 

[betwixt]

OK, it's the Olimex development board which should be OK.

I need to establish where the problem lies, it may be that the software you are using has a fault, the PIC isn't being programmed properly or the PC isn't talking to the USB port. Any of these will cause the symptom you describe. Can you answer these questions please:

1. When you connect the PIC to the programmer does it recognize the PIC and does it verify the code was written to it properly?
2. Are you programming the PIC in a socket on the 182 board or through the ICSP connection on the Olimex board? If using ICSP how long are the wires you are using?
3. When the PIC is in the Olimex board and it is powered up, can you measure the voltage across C5 (pin 18 of the PIC) and tell me what it is?

Brian.

 

[varunme]

Answers
1. The programmer recognizes the PIC and verifies the code properly.
2. I am programming through ZIF socket.
3. Volatage across pin 18 in 5V.

varun

 

[betwixt]

Somethng is wrong around pin 18. Please see page 383 of the data sheet which explains the parameters of the internal USB voltage regulator. It states the voltage must be between 3.0 and 3.6V for the USB module to operate. The capacitor on pin 18 (C5) is across the output of the internal 3.3V regulator so it it has 5V across it the regulator is probably damaged.

Brian.

 

[varunme]

so my pic is damaged , isnt it ?

 

[betwixt]

It would seem so, I'm not sure what else it could be,

It is possible to disable the internal regulator but as far as I know the voltage would drop to zero if that was done. Pin 18 is connected to tihe internal supply line to the USB module so exceeding 3.6V would almost certainly damage that part of the PIC. The remainder of the circuits are probably OK as they run on 5V anyway so the IC isn't lost, it should still work in other applications but not when USB is needed.
As a last resort, you could try disabling the internal regulator and feeding 3.3V in from outside but it's extra hardware with no guarantee it would fix the problem. If you want to try it, connect a 3.3V Zener diode from pin 18 to ground and a 100 Ohm resistor from pin 18 to +5V. You will also have to disable the internal regulator.

Brian.

 

[varunme]

can it because of bad connections ?,
originally it was connected with two 0.1 AEC caps , when it was not working , i removed it and connected with two 220nF caps .

 

[betwixt]

Microchip's data sheet says use a value no lower than 220nF and no higher than 12uF, suggesting 470nF is a good value to use. It is possible but unlikely that running with less than the minimum value made the internal regulator unstable and it went over-voltage causing damage. I'm not sure what an AEC capacitor is but again the datasheet tells you to use one with low ESR, preferably ceramic and connected with short wires.

Brian.

 

[varunme]

thank you betwixt , for helping me this much ,
ur contribution in this thread will help noobs immensely
I will buy a new Pickit 3 or a pickit clone and try my work in that
thanks
varun

 

[varunme]

Thanks for all in making time for helping me ,
the problem is solved as

https://www.edaboard.com/threads/223407/