Rabbit 2000, Руководство пользователя

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User’s Manual 9
Table 2-1 provides estimates of the operating power for selected clock speeds.
2.2.3 Time/Date Oscillator
The 32.768 kHz oscillator drives an external 32.768 kHz quartz crystal. The 32.768 kHz
clock is used to drive a battery-backable (there is a separate power pin) internal 48-bit
counter that serves as a real-time clock (RTC). The counter can be set and read by soft-
ware and is intended for keeping the date and time. There are enough bits to keep the date
for more than 100 years. The 32.768 kHz oscillator is also used to drive the watchdog
timer and to generate the baud clock for serial port A during the cold boot sequence.
2.2.4 Parallel I/O
There are 40 parallel input/output lines divided among five 8-bit ports designated A
through E. Most of the port lines have alternate functions, such as serial data or chip select
strobes. Parallel ports D and E have the capability of timer-synchronized outputs. The out-
put registers are cascaded.
Figure 2-1. Cascaded Output Registers for Parallel Ports D and E
Stores to the port are loaded in the first-level register. That register in turn is transferred to
the output register on a selected timer signal. The timer signal can also cause an interrupt
that can be used to set up the next bit to be output on the next timer pulse. This feature can
be used to generate precisely controlled pulses whose edges are positioned with high accu-
racy in time. Applications include communications signaling, pulse width modulation and
driving stepper motors.
Table 2-1. Operating Power Estimates at Selected Clock Speeds
Clock Speed
(MHz)
Voltage
(V)
Current
(mA)
Power
(mW)
Clock Speed
(MHz)
Voltage
(V)
Current
(mA)
Power
(mW)
25.0 5.0 80 400 6.0 2.5 10 25
12.5 5.0 40 200 3.0 2.5 5 12
12.5 3.3 26 87 1.5 2.5 2.5 6
6.0 3.3 13 42 0.032 2.5 0.054 0.135
Timer Clock
Load Clock
Load Data
Port Output