Rabbit Rabbit 4000, Руководство пользователя

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Chapter 4 System Management 33
4.2 Dependencies
4.2.1 I/O Pins
The CLK, STATUS, /WDTOUT, and /BUFEN pins are controlled by GOCR. Each of
these pins can be used as general-purpose outputs by driving them high or low:
•
the CLK pin can output the peripheral clock, the peripheral clock divided by two, or be
driven high or low;
•
the STATUS pin can be active low during the first byte of each opcode fetch, active low
during an interrupt acknowledge, or driven high or low;
•
the /WDTOUT pin can be active low whenever the watchdog timer resets the device or
driven low; and
•
the /BUFEN pin can be active low during external I/O cycles, active low during data
memory cycles, or driven high or low.
The values in the battery-backed onchip-encryption RAM bytes are cleared If the signal
on the SMODE pins changes state.
4.2.2 Clocks
The periodic interrupt, real-time clock, watchdog timer, and secondary watchdog timer
require the 32 kHz clock.
4.2.3 Interrupts
The periodic interrupt is enabled in GCSR, and will occur every 488 µs. It is cleared by
reading GCSR. It can operate at Priority 1, 2, or 3.
The secondary watchdog interrupt will occur whenever the secondary watchdog is
enabled and allowed to count down to zero. It is cleared by restarting the secondary watch-
dog by writing to WDTCR. The secondary watchdog interrupt always occurs at Priority 3.