668-0003-C Rabbit Semiconductor, 668-0003-C Datasheet - Page 175

• Manufacturer Part Number: 668-0003-C
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0003-C

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Features: -
• Other names: 316-1004; 668-0003

17. O
R
S
THER
ABBIT
OFTWARE
17.1 Power Management Support
The power consumption and speed of operation can be throttled up and down with rough
synchronism. This is done by changing the clock speed or the clock doubler. The range of
control is quite wide: the speed can vary by a factor of 16 when the main clock is driving
the processor. In addition, the main clock can be switched to the 32.768 kHz clock. In this
case, the slowdown is very dramatic, a factor of perhaps 500. In this ultra slow mode, each
clock takes about 30 µs, and a typical instruction takes 150 µs to execute. At this speed,
the periodic interrupt cannot operate because the interrupt routine would execute too
slowly to keep up with an interrupt every 16 clocks. Only about 3 instructions could be
executed between ticks.
A different set of rules applies in the ultra slow or “sleepy” mode. The Rabbit 2000 auto-
matically disables periodic interrupts when the clock mode is switched to 32 kHz or one of
the multiples of 32 kHz. This means that the periodic-interrupt hardware does not function
when running at any of these 32 kHz clock speeds simply because there are not enough
clock cycles available to service the interrupt. Hence virtual watchdogs (which depend on
the periodic interrupt) cannot be used in the sleepy mode. The user must set up an endless
loop to determine when to exit sleepy mode. A routine,
, is provided to
updateTimers()
update the system timer variables by directly reading the real-time clock and to hit the watch-
dog while in sleepy mode. If the user’s routine cannot get around the loop in the maximum
watchdog timer time-out time, the user should put several calls to
in
updateTimers()
the loop. The user should avoid indiscriminate direct access to the watchdog timer and
real-time clock. The least significant bits of the real-time clock cannot be read in ultra
slow mode because they count fast compared to the instruction execution time. To reduce
bus activity and thus power consumption, it is useful to multiply zero by zero. This
requires 12 clocks for one memory cycle and reduces power consumption. Typically a
number of
instructions can be executed between each test of the condition being
mul
waited for.
Dynamic C libraries also provide functions to change clock speeds to enter and exit sleepy
mode. See the Rabbit 2000 Designer’s Handbook chapter Low Power Design and Sup-
port for more details.
Chapter 17 Other Rabbit Software
169