Hi everyone,

 I have another quirk that's really horrid in the 18F458. It's a rather
difficult problem to explain, so I will attempt my best to do so.

 My boss picked up an errata note from Microchip in the 18FXX8 document for
Rev. B4 (Note numbers 4 and 5) that basically involved erratic code while
crossing the 0x4000 boundary. That means any call's or goto's from the high
section to the low section, or vice versa, had a potential to act
erraticaly. In response to this, he emailed Microchip, and they replied
stating to implement this:

Basically make intermediate functions, foo_asm, written in assembly, that
look like this:

foo_asm:
 data 0xffff
 goto real_foo

Where real_foo is written in C, located somewhere else. The "access"
function, foo_asm, would be in the same region as the calling function.. so
if I had a function in the high region of code (0x4000 and up), that needed
to call/goto foo which is in the low section (0->4000), it would call
foo_asm, which is located low section. This then calls the real function. So
far so good?

 He decided to implement this by modifying all of our function calls this
way - using access functions, splitting our code essentially into high and
low sections. Ater this, a huge problem started to happen. The INTCON
register, specifically the Low interrupt enable bit (Bit 6) was mysteriously
getting cleared after the chip was reset. No code was doing this, and I
verified by stepping through each line tediously. IT would get cleared at
various different points, purely random. I did notice that it worked on some
of our boards though. Taking a closer look at the chips, and then testing
with 12 chips in all, I found that the code, after it was split, worked on
all chips marked:

PIC18F458-I/P
0234HQB

BUT didn't work on all chips marked:

PIC18F458-I/P
0303OUE

 Could anyone shed light on this problem? We would like to get the code
working on all versions, but can't seem to do so at this point. Thank you
for your time,


Jai Dhar
Sterner Automation Limited
43 Hanna Avenue
Toronto, Ontario
M6K 1X6
416-538-1826 x231
jai.dhar@sternerautomation.com
http://www.sternerautomation.com

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