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24.3
Medium-Speed Mode
In high-speed mode, when the SCK2 to SCK0 bits in SCKCR are set to 1, the operating mode
changes to medium-speed mode as soon as the current bus cycle ends. In medium-speed mode, the
CPU operates on the operating clock (ø/2, ø/4, ø/8, ø/16, or ø/32) specified by the SCK2 to SCK0
bits. The bus masters other than the CPU (the DMAC and DTC) also operate in medium-speed
mode. On-chip supporting modules other than the bus masters always operate on the high-speed
clock (ø).
In medium-speed mode, a bus access is executed in the specified number of states with respect to
the bus master operating clock. For example, if ø/4 is selected as the operating clock, on-chip
memory is accessed in 4 states, and internal I/O registers in 8 states.
Medium-speed mode is cleared by clearing all of bits SCK2 to SCK0 to 0. A transition is made to
high-speed mode and medium-speed mode is cleared at the end of the current bus cycle.
If a SLEEP instruction is executed when the SSBY bit in SBYCR is cleared to 0, and LSON bit in
LPWRCR is cleared to 0, a transition is made to sleep mode. When sleep mode is cleared by an
interrupt, medium-speed mode is restored.
When the SLEEP instruction is executed with the SSBY bit = 1, LPWRCR LSON bit = 0, and
TCSR (WDT1) PSS bit = 0, operation shifts to the software standby mode. When software
standby mode is cleared by an external interrupt, medium-speed mode is restored.
When the RES and MRES pins are set Low and medium-speed mode is cancelled, operation shifts
to the reset state. The same applies in the case of a reset caused by overflow of the watchdog
timer.
When the STBY pin is driven low, a transition is made to hardware standby mode.
Figure 24-2 shows the timing for transition to and clearance of medium-speed mode.
866
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