Fri Oct 26 08:58:57 EDT 2012

18F2550 voltage

From the datasheet:

  1.2 Other Special Features

  Like all Microchip PIC18 devices, members of the
  PIC18F2455/2550/4455/4550 family are available as both standard and
  low-voltage devices. Standard devices with Enhanced Flash memory,
  designated with an “F” in the part number (such as PIC18F2550),
  accommodate an operating VDD range of 4.2V to 5.5V.  Low-voltage
  parts, designated by “LF” (such as PIC18LF2550), function over an
  extended VDD range of 2.0V to 5.5V.

This makes no sense.  It's an F part (not LF) runs fine on lower
voltage but not on higher voltage..  WTF?  Also, later in the DS the
operating voltage is mentioned to be a larger range:
28.1 DC Characteristics: 2.0-5.5V

Let's replace the chip and see what it does.

EDIT: Maybe this is really an LF device that's marketed as an F
device.  I assume they are the same die but get sorted into 2 range

Some discussion here[1].  People think indeed they are the same chips
passing some extra testing.  Verified by some F parts working at LF

[1] http://www.electro-tech-online.com/microcontrollers/130612-difference-between-pic-lf-pic-f.html