Rabbit 2000™ Microprocessor - UTN

2.3 Power ConsumptionWhen minimum power consumption is required, a 3.3 V power supply and a 3.6864 MHz or a1.8432 MHz crystal will usually be good choices. Such a system can operate at the main 3.6864MHz or 1.8432 MHz frequency either doubled or divided by 8 (or both). A further reduction inpower consumption at the expense of computing speed can be obtained by adding memory waitstates. Operating at 3.6864 MHz, such a system will draw approximately 11 mA at 3.3 V, notincluding the power required by the memory. Approximately 2 mA is used for the oscillator and 9mA is used for the processor. Reducing the processor frequency will reduce current proportionally.At 1/4th the frequency or (0.92 MHz) the current consumption will be approximately 4 mA.At 1/8th the frequency, (0.46 MHz) the total power consumption will be approximately 3 mA, notincluding the memories. Doubling the frequency to 7.37 MHz will increase the current to approximately20 mA.If the main oscillator is turned off and the microprocessor is operated at 32.768 kHz from theclock oscillator, the current will drop to about 200 µA exclusive of the current required by thememory. The level of power consumption can be fine-tuned by adding memory wait states, whichhave the effect of reducing power consumption. In order to obtain microampere level power consumption,it is necessary to use auto powerdown flash memories to hold the executing code.Standby power while the system is waiting for an event can be reduced by executing long stringsof multiply zero by zero instructions. Keep in mind that a Rabbit operating at 3.68 MHz has thecompute power of a Z180 microprocessor operating at approximately triple the clock frequency(11 MHz).2.4 Through-hole TechnologyMost design advice given for the Rabbit assumes the use of surface-mount technology. However,it is possible to use the older through hole technology and develop a Rabbit system. One can useZ-World’s Rabbit-based Core Module, a small circuit board with a complete Rabbit core thatincludes memory and oscillators. Another possibility is to solder the Rabbit processors by hand tothe circuit board. This is not difficult and is satisfactory for low production volumes if the righttechnique is used.Designer’s Handbook 5