Digi Rabbit 5000, User Manual

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342 Rabbit 5000 Microprocessor User’s Manual
Depending on the application, the processor can continue executing code normally when
the main oscillator is divided down to a lower value. However, when the processor clock
is running off of the 32 kHz clock, it is recommended that the Rabbit 5000 be performing
a tight polling loop, waiting for a wake-up event.
29.2.3 Short Chip Selects
When running at a reduced clock speed, it is likely that the chip selects for external
devices will not need to be active for an entire clock cycle. By reducing the width of the
chip select, the power consumption of the memory chip can be reduced without having
any affect on the processor itself.
For reduced processor speeds based on the main oscillator, a short chip select can be
enabled in GPSCR (this feature is not available when the processor is running at full
speed). This feature can be enabled separately for both reads and writes. When enabled,
the chip select signals will be the width of two undivided clocks and located at the end of
the transaction. The read data in the figures below is sampled by the rising edge of CLKI
that terminated the T2 cycle. Wait states are inserted between T1 and T2 so they do not
affect the width of the strobe.
CLK1
CLK
A[23:0]
D[7:0]
/CSx
/OEx
valid
T1 T2
Divide by 8 Mode