Rabbit 2000™ Microprocessor - UTN

10. Memory PlanningThe following requirements should be considered when planning memory configuration for a Rabbitsystem.• The size of the code anticipated. Usually code size up to 512K is handled by one flash memorychip. Static data tables can be conveniently placed in the same space using the xdata andxstring declarations supported by Dynamic C, so the amount of space needed for static datacan be added to the amount of space needed for code. If you are writing a program from scratch,remember that 512K of code is equivalent to 25,000 to 50,000 C statements, and such a largeprogram can take years to write.• C programs vary in how much RAM will be required. Many programs can subsist on 32K ofRAM. Having more RAM on the system is convenient for debugging since debugging and programtesting generally operates more powerfully and faster when sufficient RAM is available tohold the program and data. For this reason, most Z-World controllers based on the Rabbit use adual footprint for RAM that can accommodate either a 32K x 8, which is in a 28-pin package, ora 128K x 8 or 512K x 8, which is in a 32-pin package. The base RAM is 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 toaccommodate programs.RAM for extended memory—such as data logging applications or communicationsapplications. The amount needed depends on application.10.1 Making a RAM-only board.Some Rabbit customers are designing boards that have only a single RAM chip and no flash memory.Although this is not generally recommended, it may be safe to use only a RAM chip as longas the board has a continuous power supply and is set up to be field-programmable via the Rabbitbootstrap mode.For example, a Rabbit board in a noncritical system such as a lawn sprinkler system may be monitoredfrom a remote location via the Internet or Ethernet, where the remote monitor has the abilityto reload the application program to the board. One way to achieve field programmability is withthe RabbitLink Network Gateway.There are certain hardware and software changes that are required to make this work which arediscussed here. Dynamic C starting with version 6.57 has the software files discussed here whichare necessary to make a RAM only board work.Designer’s Handbook 51