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Designer’s
Handbook
33
9.
Memory Planning
The
following requirements should be considered when planning memory configuration
for
a Rabbit system.
•
The
size of the code anticipated. Usually code size up to 512K is handled by one flash
memory
chip. Static data tables can be conveniently placed in the same space using the
xdata
and
xstring
declarations supported by Dynamic C, so the amount of space
needed
for static data can be added to the amount of space needed for code. If you are
writing
a program from scratch, remember that 512K of code equivalent to 25,000 to
50,000
C statements, and such a large program can require man years to write.
•
C
programs vary in how much RAM memory will be required. Many programs can
subsist
on 32K of RAM. Having more RAM on the system is convenient for debug-
ging
since debugging and program testing generally operates more powerfully and
faster
when sufficient RAM is available to hold the program and data. For this reason,
most
Z-World controllers based on the Rabbit use a dual footprint for RAM that can
accommodate
either a 32K x 8, which is in a 28-pin package, or a 128K x 8 or 512K x
8,
which is in a 32-pin package. The base RAM is always interfaced to /CS1 and
/WE1,
and /OE1. RAM is required for the following items.
Root
variables—maximum of 48K.
Stack
pages—rarely more than 20K.
RAM
for debugging convenience on prototype units—512K is usually enough to
accommodate
programs.
RAM
for extended memory, such as data logging applications or communications
applications—amount
needed depends on application.
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