PIC18F2550-I/SP programming issues

[The_JinJ]

Hi

I've had a read through other threads where people have had issues with programming the PIC but no joy finding a solution so far.

I have checked my board fro shorts etc and all is ok - I think the problem is that Pin 14 has 0V (which I believe should be supplied 3.3v internally) - +5v is ok on Pins 1 and 20 and all ones that should be 0v are ok.

Not sure what could be at fault (this is a new PIC) - I have a crystal amd caps I could replace if this could be the issue? Any pointers would be much appreciated.

Thanks
Neil

EDIT
I have the Atmega324 programmed and functioning ok

[Firelord]

Hi

I've had a read through other threads where people have had issues with programming the PIC but no joy finding a solution so far.

I have checked my board fro shorts etc and all is ok - I think the problem is that Pin 14 has 0V (which I believe should be supplied 3.3v internally) - +5v is ok on Pins 1 and 20 and all ones that should be 0v are ok.

I've had trouble with my PIC due to not cleaning the board good enough after soldering. Also you should try taking PIC out of its socket, cleaning its pins with alcohol and putting it back. Sometimes this helps.

[dmitri]

http://www.google.co.uk/search?hl=en&q= ... =&aq=f&oq=

In a nut shell:
1. Faulty PIC
2. Soldering problems - shorts/breaks/flux residue
3. Faulty parts around PIC

[The_JinJ]

http://www.google.co.uk/search?hl=en&q=pic18f2550+site%3Awww.megadrum.info%2Fforums&btnG=Search&meta=&aq=f&oq=

In a nut shell:
1. Faulty PIC
2. Soldering problems - shorts/breaks/flux residue
3. Faulty parts around PIC

Thanks

Any clue to which faulty parts could cause the 0v (if there are no shorts)? I assume the cap on pin 14 to ground shouldn't affect this as measuring direct from the pin to rail gives 0v - can the crystal be responsible?

[dmitri]

http://www.google.co.uk/search?hl=en&q=pic18f2550+site%3Awww.megadrum.info%2Fforums&btnG=Search&meta=&aq=f&oq=

In a nut shell:
1. Faulty PIC
2. Soldering problems - shorts/breaks/flux residue
3. Faulty parts around PIC

Thanks

Any clue to which faulty parts could cause the 0v (if there are no shorts)? I assume the cap on pin 14 to ground shouldn't affect this as measuring direct from the pin to rail gives 0v - can the crystal be responsible?

A faulty cap (internal short) can cause it. Shorts in the crystal also can cause it but I can't tell it for sure since I haven't had faulty crystals or caps for that matter.

[The_JinJ]

I'm a bit confused, reading the spec the USB module should be enabled (USBEN <UCON, bit3> = 1) and USB internal Voltage regulator also enabled in the configuration bits (VREGEN <CONFIG2L, bit5> = 1) - it seems without this then pin 14 shouldn't have 3.3v - so does it need programmed first??

[dmitri]

Good point, 3.3v really might be present on this pin only when PIC is programmed but I cannot check it right now.

[dmitri]

Checked the documentation for PIC18F2550 and this is what it says:

The regulator is enabled by default and can be disabled
through the VREGEN Configuration bit. When enabled,
the voltage is visible on pin VUSB. When the regulator
is disabled, a 3.3V source must be provided through
the VUSB pin for the internal transceiver. If the internal
transceiver is disabled, VUSB is not used.

So there must be 3.3v on pin 14 of a brand new PIC18F2550.

[dmitri]

Well, it was an old version of the datasheet pdf I looked into. In the latest version it says:

The regulator can be enabled or disabled through the
VREGEN Configuration bit. When enabled, the voltage
is visible on pin VUSB whenever the USBEN bit is also
set. When the regulator is disabled (VREGEN = 0), a
3.3V source must be provided through the VUSB pin for
the internal transceiver.

and also by default VREGEN=0 so after all regardless of USBEN a brand new PIC18F2550
will have 0v on pin 14.

[jman 31]

If I remember right, I finally tried a different pc to get mine working. Not positive though.