52 Rabbit 2000 Microprocessor5.3 Rabbit Pin DescriptionsTable 5-1 lists all the pins on the device, along with their direction, function, and pin num-ber on the package.Table 5-1. Rabbit Pin DescriptionsPin Group Pin Name Direction Function Pin NumbersHardwareCLK OutputPeripheral clock output. This signal isderived internally from the main systemoscillator as perclk, and may be dividedby 8, doubled, or both, by programmableinternal circuitry. This signal is enabledafter reset. Under program control, this pincan output the full internal clock frequency,or 1/2 the internal frequency, or it can beused as a general-purpose output pin undersoftware control. See Table 7-3, “GlobalOutput Control Register (GOCR = 0x0E).”1/RESET Input Master reset. 37XTALA1 InputQuartz crystal for 32 kHz clock oscillator.Lines to the crystal should be short andshielded from crosstalk. If an externalclock is used, this pin should be driven bythe external clock.40XTALA2 Output Quartz crystal for 32 kHz crystal oscillator.Do not connect if an external clock is used. 41XTALB1 InputQuartz crystal for main system oscillator.Lines to the crystal should be short andshielded from crosstalk. If an externalclock is used this pin should be driven bythe external clock.90XTALB2 Output Quartz crystal for main system oscillator.Do not connect if an external clock is used. 91CPU BusesA0–A19 Output Address bus. 7, 17–20, 61–68, 70–75, 79D0–D7 Bidirectional Data bus. 9–16Status/Control /WDTOUT OutputWDT timeout—outputs a pulse when theinternal watchdog times out. May also beused to output a 30 μs pulse.34Status STATUS OutputProgrammable for functions:1. driven low on first opcode fetch cycle2. driven low during interruptacknowledge cycle3. to serve as a general-purpose output.See Table 7-3, “Global Output ControlRegister (GOCR = 0x0E).”.38
