18F4550 Not Recognised

[Demon]

Hi,

There is a capacitor connected to Vusb in figure 17.10 on page 184 of the datasheet for the PIC 18F4550.

But I can't find any reference to the recommended value, where did you guys come up with 400nF? And how much more than 400nF can we go?

Robert

[Demon]

Ok, I found another thread where Melanie mentions 17.2.2.8:

"The PIC18FX455/X550 devices have a built-in 3.3V regulator
to provide power to the internal transceiver and
provide a source for the internal/external pull-ups. An
external 220 nF (±20%) capacitor is required for stability."

I don't know why people are mentionning 400nF when the datasheet states 220nF, give or take 20%. Either way, I don't have capacitors in this range so I'm stuck for now.

Robert

[mister_e]

higher value may be needed if you experiment some erratic connection failure.

As now, 220nF work great for the really few USB stuff i did as now. you can even place two 220nF (0.22uF) in parrallel or a match of to get the value you want in meantime.

Robert.. OT but KGE will move in the next days/months in the old FLY store near the 30. Will be by far bigger

[Christopher4187]

400nF comes from experience. I know what the datasheet says but with 220nF, I found the 18F4550 had trouble enumerating. It may have been due to my design and for most people 220nF may work fine but I was just giving my experience. I don't think there is any harm in using a higher value cap.

[Demon]

Did you get something like this when you didn't have the proper capacitor value?

First the device is seen, but then it craps out with an error.

Robert

[mister_e]

could be that. probably you should try first to remove all HIDs in the Control panel/System/Hardware/DeviceManager while your unit is connected and then reboot, then retry.

It may also be a Microchip Bootloader problem if you use it. If so, erease the best, reprogram your device without the bootloader, then retry... about now?

If the problem is the Bootloader, be sure you place a pull-up on PORTB.4 and it may solve some problem. When booting, it looks if the PORTB.4 is low to enter the programming mode. So if your pin is floating it may just ruine your life.

I may be out but try this and the capacitor stuff.

Make sure you keep the connection alive every few mSec with the USBSERVICE.

[Demon]

...

Robert.. OT but KGE will move in the next days/months in the old FLY store near the 30. Will be by far bigger

Steve, can you give me more details, I don't know the FLY store. If King George Electronics moves closer to the 30 it's great for me, less distance to travel to buy emergency parts (like a 220nF cap).

Robert

[mister_e]

Robert, Fly is besing the Golf.... between the St-Bruno shopping center and Boulevard Cousineau.. on the voie de service. It will be done in few days week. In meantime, MasterVox at Longeuil.

[Demon]

I'm not using a bootloader, don't know how.

I have a pull-up on B4.

I have USBSERVICE in the loop, my code was generated with HIDMaker FullSpeed.

I don't have the Vusb cap, I have to go buy a couple values.

Robert

[mister_e]

what are the value you have? Any scrapped computer, printer or anything else electronic?

Look for it in there... that's free.. if you don't calculate your time, movement, gas and plah plah plah.

[mister_e]

one thing that just spring to mind... what about your main loop?

Is there some USBIN? if so, remove it and just send few data to know.. what happen now?

[Bruce]

I use 470nF on all my USB boards, and have never had a problem with any. That's the same value used on the MeLabs and Microchip USB development boards.