Hi all. I've come up against a part of the PIC that I find really hard
to understand. So I'm going to give my interpretation, then hopefully
you can correct me where I am wrong. Basically this involves the
differences between the PCL and jump tables, and the FSR and indirect
addressing.

To use the FSR, basically you load an address into it, for example 0x50.
Then you can access that memory location using INDR right? And if I do
something like "incf fsr" I can now access 0x51 right? As far as I can
tell, this would be usefull for storing a bunch of variables and then
recalling them later. The advantage is I can change memory locations
easily (by modifying the FSR), and if needed I can access the data out
of order. However, if I wanted to set up some sort of table or something
using the FSR, at the beginning of my code, I'd have to load the data
into the table, or it would be empty (or random).

Now, the PCL I know less about. The basic idea as I understand it is
that dependant on some sort of decision, I can load a value into the PCL
and then on the next instruction, program execution will continue from
that location. But how do I know what value to load? Do I just use any
open value, then put an ORG instruction in front of the code that I want
there? How do I return to my main code again? Ok, questions aside, the
advantages here would be that I could have large tables and that they
could live in program memory, and not take up valuable data memory
right? But how do I deal with program memory banks? I have never figured
that out either. How do I know when I need to switch banks?

Now let me explain my project. Basically what I will need to do is to
take an eight bit number, and convert it to another 8 bit number that
will then be used in the TMR to give me a specific delay. So what I
think I should use is the PCL because I don't have 256 bytes of data
memory. I want to use a table so that I can change the relationship
between the delay and the input number if needed. Question is, how do I
do this? Are there any tutorials out there about this? I'd really
appreciate any help anyone can give.

Thanks!

Josh Koffman

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