Rabbit 2000 - 2.2 Overview of On-Chip Peripherals

10 Rabbit 2000 Microprocessor
this degree of control is not desired for a particular situation, then certain pins can be
left unconnected in the connecting cable, limiting the functionality of the connector to
serial communications. Z-World will be developing products and software that assume
the presence of the programming connector.
• Dynamic C and a PC are not necessarily needed for the production programming of
flash memory since the flash memory can be copied from one controller to another by
cloning. This is done by connecting the system to be programmed to the same type of
system that is already programmed by means of a cloning cable. The cloning cable con-
nects to both programming ports and has a button to start the transfer of program and an
LED to display the progress of the transfer.
Dynamic C programming uses the Rabbit’s serial port A for software development. How-
ever, it is still possible, with some restrictions, for the user’s application to also use port A.
4.1 Memory Organization
The Rabbit architecture is derived from that of the original Z80 microprocessor. The orig-
inal Z80 instruction set used 16-bit addresses to address a 64K memory space. All code
and data had to fit in this 64K space. The Rabbit adopts a scheme similar to that used by
the Z180 to expand the available memory space. The 64K space is divided into zones and
a memory mapping unit or MMU maps each zone to a block in a larger memory; the larger
memory is 1 megabyte in the case of the Z180 or the Rabbit 2000. The zones are effec-
tively windows to the larger memory. The view from the window can be adjusted so that
the window points to different blocks in the larger memory. Figure 2 on page 12 shows the
memory mapping schematically.
The Rabbit has a basic 20-bit or 1-megabyte physical memory space. In special circum-
stances more than 1-megabyte of memory can be installed and accessed using auxiliary
memory mapping schemes. Typical Rabbit systems have two types of physical memory—
flash memory and static RAM memory. Flash memory follows a write once in a while and
read frequently model. Depending on the particular type of flash used, the flash memory
will wear out after it has been written around 10,000 to 100,000 times.
Rabbit flash memory may be small-sector type or large-sector type. Small-sector memory
typically has sectors of 128 or 256 bytes. Individual sectors may be separately erased and
written. In large-sector memory the sectors are often 16K or 64K or more. Small-sector
memory provides better support for program development and debugging, and large-sec-
tor memory is less expensive and has faster access time. The best solution will usually to
lay out a design to accept several different types of flash memory, including the flexible
small-sector memories and the fast large-sector memories. At the present time develop-
ment support for programs tested in flash memory is confined to flash memories with sec-
tors of 256 bytes or 128 bytes. If larger sectors are used, the code must be debugged in
RAM and then loaded to flash for a final test that does not involve setting break points. In
future releases it is planned to support direct debugging in large-sector flash. Large-sector
flash is desirable for the better access time and power consumption specifications that are
available.