668-0011 Rabbit Semiconductor, 668-0011 Datasheet - Page 17

• Manufacturer Part Number: 668-0011
• Description: IC MPU RABIT3000A 55.5MHZ128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0011

• 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: 316-1043

2. C
LOCKS
2.1 Overview
The Rabbit 3000 supports two separate clocks—the main clock and the 32 kHz clock. The
main clock is used to derive the processor clock and the peripheral clock inside the proces-
sor. The 32 kHz clock is used to drive the asynchronous serial bootstrap, the real-time
clock, the periodic interrupt, and the watchdog timers.
The Rabbit 3000 has a spectrum spreader on the main clock that shortens and lengthens
clock cycles. This has the net effect of reducing the peak energy of clock harmonics by
spreading the spectral energy into nearby frequencies, which reduces EMI and facilitates
government-mandated EMI testing. Gated clocks are used whenever possible to avoid
clocking unused portions of the processor, and separate power-supply pins for the core and
I/O ring further reduce EMI from the Rabbit 3000.
The main clock can be doubled or divided by 2, 4, 6, or 8 to reduce EMI and power con-
sumption. The 32 kHz clock (which can be divided by 2, 4, 8, or 16) can be used instead of
the main clock to generate processor and peripheral clocks as low as 2 kHz for significant
power savings. Note that dividing the 32 kHz clock only affects the processor and periph-
eral clocks; the full 32 kHz signal is still provided to the peripherals (RTC and watchdog
timers) that use it directly. The periodic interrupt is automatically disabled since there is
not enough time to process it when running off the 32 kHz clock.
Chapter 2 Clocks
7