Z180

The Rabbit is an evolutionary design. The instruction set and the register layout is that of the Z80 and Z180. The instruction set has been augmented by a substantial number of new instructions. Some obsolete or redundant Z180 instructions have been dropped to make available efficient 1-byte opcodes for important new instructions. (see "Differences Rabbit vs. Z80/Z180 Instructions" on page 187.) The advantage of this evolutionary approach is that users familiar with the Z80 or Z180 can immediately understand the Rabbit. Existing source code can be assembled or compiled for the Rabbit with minimal changes.

Changing technology has made some features of the Z80/Z180 family obsolete, and these have been dropped. For example, the Rabbit has no special support for dynamic RAM but it has extensive support for static memory. This is because the price of static memory has decreased to the point that it has become the preferred choice for medium-scale embedded systems. The Rabbit has no support for DMA (direct memory access) because most of the uses for which DMA is traditionally used do not apply to embedded systems, or they can be accomplished better in other ways, such as fast interrupt routines, external state machines or slave processors.

Our experience in writing C compilers has revealed the shortcomings of the Z80 instruction set for executing the C language. The main problem is the lack of instructions for handling 16-bit words and for accessing data at a computed address, especially when the stack contains that data. New instructions correct these problems.

Another problem with many 8-bit processors is their slow execution and a lack of numbercrunching ability. Good floating-point arithmetic is an important productivity feature in smaller systems. It is easy to solve many programming problems if an adequate floatingpoint capability is available. The Rabbit's improved instruction set provides fast floatingpoint and fast integer math capabilities.

The Rabbit supports four levels of interrupt priorities. This is an important feature that allows the effective use of super fast interrupt routines for real-time tasks.

• Motion Controller-Many types of motion control require fast action, may be compute-intensive or both. Traditional servo system solutions may be overly expensive or not work very well because of system nonlinearities. The basic communications model for a motion controller is for the master to send short messages-positioning commands- to the slave. The slave acknowledges execution of the commands and reports exception conditions.
• Communications Protocol Processor-Communications protocols may be very complex,may require fast responses, or may be compute-intensive.
• Graphics Controller-The Rabbit can be used to perform operations such as drawing geometric figures and generating characters.
• Digital Signal Processing-Although the Rabbit is not a speciality digital signal processor,it has enough compute speed to handle some types of jobs that might otherwise require a speciality processor. The slave processor can process data to perform pattern recognition or to extract a specific parameter from a data stream.

TA Operating Temperature ...................-55°C to +85°C
TS Storage Temperature ....................-65°C to +150°C
Maximum Input Voltage*...............-0.6 to (VDD + 0.75) V
VDD Maximum Operating Voltage ............................6.0 V
Max Current Through Input Protection Diodes...... 5.0 mA
* The minimum voltage is -0.6 V DC, which may undershoot to -2.0 V for pulses that are shorter than 20 ns. The maximum output pin voltage is VDD + 0.75 V DC, which may overshoot for pulses that are shorter than 20 ns.