668-0010 Rabbit Semiconductor, 668-0010 Datasheet - Page 26

• Manufacturer Part Number: 668-0010
• Description: IC MPU RABIT3000 55.5MHZ 128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0010

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 3000 8-Bit
• Speed: 55.5MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Features: -
• Other names: 316-1016

2.3.4 32 kHz Clock
The 32.768 kHz clock is used to drive the asynchronous serial bootstrap, the real-time
clock, the periodic interrupt, and the watchdog timers. If these features are not used in a
design, the use of the 32 kHz clock is optional.
A simplified version of the recommended oscillator circuit for the Rabbit 3000 is shown
below. The values of resistors and capacitors may need to be adjusted for various frequen-
cies and crystal load capacitances. Rabbit’s Technical Note TN235, “External 32.768 kHz
Oscillator Circuits,“ is available on the Rabbit Web site and goes into this circuit in detail.
Figure 2-4. Basic 32.768 kHz Oscillator Circuit
The 32.768 kHz circuit consumes microampere level currents and has a very high imped-
ance, making it susceptible to noise, moisture, and environmental contaminants. It is
strongly recommended to conformally coat this circuit to limit effects of temperature and
humidity on the oscillation frequency. Details about this requirement are available in
Rabbit’s Technical Note TN303, “Conformal Coating”, from the Rabbit Web site.
The 32.768 kHz oscillator is slow to start oscillating after power-on. For this reason, a
wait loop in the BIOS waits until this oscillator is oscillating regularly before continuing
the startup procedure. If the clock is battery-backed, there will be no startup delay since
the oscillator is already oscillating. The startup delay may be as much as 5 seconds.
Crystals with low series resistance (R < 35 k) will start faster.
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Rabbit 3000 Microprocessor User’s Manual