I just stumbled onto a problem I can't explain.  I am using a n 18F452 an=
d generating some time delays in my application by using a simple nested =
countdown loop. So I have three variables and they are decremented in a n=
ested loop as follows:

These are the variable file definitions:


        TimerLO    equ    0x030
        TimerMD    equ    0x031
        TimerHI    equ    0x032

I load the three variables with a set of starting values and then do a mu=
ltiple loop on the three timers until they all get to zero. Fairly simple=
.

While moving things around in memory I discovered (as far as I can see) t=
hat putting the three TimerLO/MD/HI variables anywhere above the 1st page=
 0x130...0x530 causes the time delay to increase MARKEDLY - like 10X.  My=
 scope just died so I can't even continue checking this.

I can't see any reason this would happen - the 18Fxxx are supposed to acc=
ess 6 banks of register files ($0x000..$0x5ff of RAM) directly.  Or am I =
off the track here somewhere and missing something simple?  I am concerne=
d about this not because of the time delay - there are other (probably be=
tter) ways to get that.  But I was planning to move a pair of Serial I/O =
buffers up to high RAM locations and can't really think that access would=
 be that much slower off of Page 0.

Roy J. Gromlich

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