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Section 27 Power-Down Modes
27.3
Medium-Speed Mode
The CPU makes a transition to medium-speed mode as soon as the current bus cycle ends
according to the setting of the SCK2 to SCK0 bits in SBYCR. In medium-speed mode, the CPU
operates on the operating clock (φ/2, φ/4, φ/8, φ/16, or φ/32) specified by the SCK2 to SCK0 bits.
The bus masters other than the CPU (DTC or RFU) also operate in medium-speed mode when the
DTSPEED bit in SBYCR is cleared to 0. Note however that the DTSPEED bit must be set to 1
when the RFU is used in medium-speed mode. On-chip peripheral modules other than the bus
masters always operate on the system clock (φ).
When the DTSPEED bit in SBYCR or the EXCKS bit in BCSR2 is set to 1, the φ clock can be
used as the DTC/RFU operating clock or external extended area bus cycle clock.
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 φ/4 is selected as the operating clock, on-chip
memory is accessed in 4 states, and internal I/O registers in 8 states.
By clearing all of bits SCK2 to SCK0 to 0, a transition is made to high-speed mode 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 the 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 set to 1, the LSON bit cleared to 0, and the PSS bit in TCSR (WDT_1) cleared to 0,
operation shifts to software standby mode. When software standby mode is cleared by an external
interrupt, medium-speed mode is restored.
When the RES pin is 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 27.2 shows an example of medium-speed mode timing.
Rev. 3.00 Jan 25, 2006 page 781 of 872
REJ09B0286-0300
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