18F4550 Not Recognised

[Christopher4187]

Funky,

How did you make out? When I took my device from the development board to a circuit board, I had similar problems. As Bruce mentioned, a 20Mhz crystal will work good. In fact, I use a 20Mhz resonator on all of my devices because they are subject to more shock and seem to be a bit more reliable. Anyhow, I have found that if the capacitor value is not correct, you will get this error message. Check the cap on Vusb and use something that is more than 400nF. Once I changed this capacitor on Vusb, everything worked great.

Good Luck,

Chris

[Funky Gibbon]

Thanks to all for their surgestions, im not ignoring anyone, i will post results as they happen, im a bit tied down with work and stuff right now

[Funky Gibbon]

Well the update is that the chip is now working, not having a >400nf cap lying around i stuck a 330pf in Vusb instead, it's running Microchips, Mouse in a circle demo, looking at the datasheet i would not have expected that one cap to make any difference being where it is situated, but i was wrong,
Thanks to all for your help

Shaun

[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]

...

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