1. Introduction

Rabbit Semiconductor was formed expressly to design a a better microprocessor for use in small and medium-scale controllers. The first product is the Rabbit 2000 microprocessor. The Rabbit 2000 designers have had years of experience using Z80, Z180 and HD64180 microprocessors in small controllers. The Rabbit shares a similar architecture and a high degree of compatibility with these microprocessors, but it is a vast improvement.

The Rabbit has been designed in close cooperation with Z-World, Inc., a long-time manufacturer of low-cost single-board computers. Z-World's products are supported by an innovative C-language development system (Dynamic C). Z-World is providing the software development tools for the Rabbit.

The Rabbit is easy to use. Hardware and software interfaces are as uncluttered and are as foolproof as possible. The Rabbit has outstanding computation speed for a microprocessor with an 8-bit bus. This is because the Z80-derived instruction set is very compact and the design of the memory interface allows maximum utilization of the memory bandwidth. The Rabbit races through instructions.

Traditional microprocessor hardware and software development is simplified for Rabbit users. In-circuit emulators are not needed and will not be missed by the Rabbit developer. Software development is accomplished by connecting a simple interface cable from a PC serial port to the Rabbit-based target system.

1.1 Features and Specifications

• 100-pin PQFP package. Operating voltage 2.7 V to 5 V. Clock speed to 30 MHz. All specifications are given for both industrial and commercial temperature and voltage ranges. Rabbit microprocessors cost under $10 in moderate quantities.
• Industrial specifications are for a voltage variation of 10% and a temperature range from -40°C to +85°C. Commercial specifications are for a voltage variation of 5% and a temperature range from 0°C to 70°C.
• 1-megabyte code space allows C programs with up to 50,000+ lines of code. The extended Z80-style instruction set is C-friendly, with short and fast instructions for most common C operations.
• Four levels of interrupt priority make a fast interrupt response practical for critical applications. The maximum time to the first instruction of an interrupt routine is about 1 µs at a clock speed of 25 MHz.
• Access to I/O devices is accomplished by using memory access instructions with an I/O prefix. Access to I/O devices is thus faster and easier compared to processors with a restricted I/O instruction set.
• The hardware design rules are simple. Up to six static memory chips (such as RAM and flash EPROM) connect directly to the microprocessor with no glue logic. Even larger amounts of memory can be handled by using parallel I/O lines as high-order address lines. The Rabbit runs with no wait states at 24 MHz with a memory having an access time of 70 ns. There are two clocks per memory access. Most I/O devices may be connected without glue logic.
• The memory cycle is two clocks long. A clean memory and I/O cycle completely avoid the possibility of tri-state fights. Peripheral I/O devices can usually be interfaced in a glueless fashion using pins programmable as I/O chip selects, I/O read strobes or I/O write strobe pins. A built-in clock doubler allows ½-frequency crystals to be used to reduce radiated emissions.
• The Rabbit may be cold-booted via a serial port or the parallel access slave port. This means that flash program memory may be soldered in unprogrammed, and can be reprogrammed at any time without any assumption of an existing program or BIOS. A Rabbit that is slaved to a master processor can operate entirely with volatile RAM, depending on the master for a cold program boot.
• There are 40 parallel I/O lines (shared with serial ports). Some I/O lines are timer synchronized, which permits precisely timed edges and pulses to be generated under combined hardware and software control.
• There are four serial ports. All four serial ports can operate asynchronously in a variety of customary operating modes; two of the ports can also be operated synchronously to interface with serial I/O devices. The baud rates can be very high--1/32 the clock speed for asynchronous operation, and 1/6 the clock speed externally or 1/4 the clock speed internally in synchronous mode. In asynchronous mode, the Rabbit, like the Z180, supports sending flagged bytes to mark the start of a message frame. The flagged bytes have 9 data bits rather than 8 data bits; the extra bit is located after the first 8 bits, where the stop bit is normally located, and marks the start of a message frame.
• A slave port allows the Rabbit to be used as an intelligent peripheral device slaved to a master processor. The 8-bit slave port has six 8-bit registers, 3 for each direction of communication. Independent strobes and interrupts are used to control the slave port in both directions. Only a Rabbit and a RAM chip are needed to construct a complete slave system if the clock and reset are shared with the master processor
• The built-in battery-backable time/date clock uses an external 32.768 kHz crystal. The time/date clock can also be used to provide periodic interrupts every 488 µs. Typical battery current consumption is 25 µA with the suggested battery circuit. An alternative circuit provides means for substantially reducing this current.
• Numerous timers and counters (six all together) can be used to generate interrupts, baud rate clocks, and timing for pulse generation.
• The built-in main clock oscillator uses an external crystal or more usually a ceramic resonator. Typical resonator frequencies are in the range of 1.8 MHz to 29.5 MHz. Since precision timing is available from the separate 32.768 kHz oscillator, a low-cost ceramic resonator with ½ percent error is generally satisfactory. The clock can be doubled or divided by 8 to modify speed and power dynamically. The I/O clock, which clocks the serial ports, is divided separately so as not to affect baud rates and timers when the processor clock is divided or multiplied. For ultra low power operation, the processor clock can be driven from the separate 32.768 kHz oscillator and the main oscillator can be powered down. This allows the processor to operate at approximately 100 µA and still execute instructions at the rate of approximately 10,000 instructions per second. This is a powerful alternative to sleep modes of operation used by other processors. The current is approximately 65 mA at 25 MHz and 5 V. The current is proportional to voltage and clock speed--at 3.3 V and 7.68 MHz the current would be 13 mA, and at 1 MHz the current is reduced to less than 2 mA. Flash memory with automatic power down (from AMD) should be used for operation at the lowest power.
• The excellent floating-point performance is due to a tightly coded library and powerful processing capability. For example, a 25 MHz clock takes 14 µs for a floating add, 13 µs for a multiply, and 40 µs for a square root. In comparison, a 386EX processor running with an 8-bit bus at 25 MHz and using Borland C is about 10 times slower.
• There is a built-in watchdog timer.
• The standard 10-pin programming port eliminates the need for in-circuit emulators. A very simple 10 pin connector can be used to download and debug software using Z-World's Dynamic C and a simple connection to a PC serial port. The incremental cost of the programming port is extremely small.

Figure 1-1 shows a block diagram of the Rabbit.

Figure 1-1. Block Diagram of the Rabbit Microprocessor

1.2 Summary of Rabbit Advantages

• The glueless architecture makes it is easy to design the hardware system.
• There are a lot of serial ports and they can communicate very fast.
• Precision pulse and edge generation is a standard feature.
• Interrupts can have multiple priorities.
• Processor speed and power consumption are under program control.
• The ultra low power mode can perform computations and execute logical tests since the processor continues to execute, albeit at 32 kHz.
• The Rabbit may be used to create an intelligent peripheral or a slave processor. For example, protocol stacks can be off loaded to a Rabbit slave. The master can be any processor.
• The Rabbit can be cold booted so unprogrammed flash memory can be soldered in place.
• You can write serious software, be it 1,000 or 50,000 lines of C code. The tools are there and they are low in cost.
• If you know the Z80 or Z180, you know most of the Rabbit.
• A simple 10-pin programming interface replaces in-circuit emulators and PROM programmers.
• The battery backable time/date clock is included.
• The standard Rabbit chip is made to industrial temperature and voltage specifications.