18F4550 Not Recognised

[bholmen]

The thread here is a few years old but I have been seeing something with the 18F4550 that I would like others to review.

I am very new to experimenting with USB and PICs but have a number of excellent tools to help me learn. I run Pic Basic Pro 2.50, HIDmaker, have the book USB complete, write in VB 6.0, use a Melabs U2 programmer, and have the Melabs LAB-XUSB experimental board and a number of PICPROTO-USB prototyping boards populated with 18F4550's.

My preliminary test program worked well on the Lab-XUSB board but I noticed intermittent USB on the Picproto-USB boards. Realized from other discussions that the Vusb capacitor to ground was important but even with the proper capacitor the USB would connect and disconnect continuously every few seconds.

I found that I could eliminate this connection problem by changing one setting in the configuration. The setting is "Low Voltage Programming". If enabled I would have problems and disabled it works great.

This seems a little odd to me and would like to know if others can repeat this and shed some light on this subject.

I have reproduced this with 5 different boards and 5 different 18F4550's.

Bruce
Duluth, MN

I scoped out the power and when looking at Vusb I noticed it was cycling high and low (actually dropping slowly and returning high faster). My connects occurred when the voltage returned high but after dropping to around 3 volts would disconnect.

[mister_e]

This is always nice when we have the code (and schematic) to evaluate any kind of potential issue.

BUT leaving Low-Programming mode enabled is a sure way to have some issue one day or another... unless you don't use this pin and set it to GND via a pull-down resistor.

This rule apply to all PIC with Low-Voltage programming mode.

[bholmen]

Thanks for the reply. I will have to read up on the low voltage programming. I must be thinking it was different than it is. I always have the same comment you do (where is the schematic and code you are having trouble with), not so much here on this forum but on most groups I belong to. So much good advice here but also so many details to pay attention to.

Bruce