Rabbit 2000 - 9 Memory Planning

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.