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CHAPTER 6 LOW-POWER CONSUMPTION MODE
6.4 CPU Intermittent Operation Mode
6.4
CPU Intermittent Operation Mode
The CPU intermittent operation mode is a mode for reducing the power consumption by
intermittently operating the CPU while operating the external bus and peripheral
functions at high speed.
■ CPU Intermittent Operation Mode
The CPU intermittent operation mode is a mode for stopping the clock supplied to the CPU for a
predetermined period of time for each instruction execution to delay the internal bus cycle start when
accessing the registers, internal memory (ROM, RAM), I/O, peripheral functions, or external bus. If the
CPU operation speed is decreased while supplying a high-speed peripheral clock to the peripheral
functions, processing at low-power consumption becomes available.
• Selection of the number of the suspend cycles of the clock supplied to CPU is made in the CPU clock
suspend cycle number selection bit (CG1 and CG0) of the low-power consumption mode control
register (LPMCR).
• The external bus operation itself uses the same clock as the peripheral functions.
• The instruction execution time in CPU intermittent operation mode can be calculated by adding to the
ordinary execution time the compensation value obtained by multiplying the instruction execution count
for accessing the registers, internal memory, internal peripheral function, and external bus by the
number of suspension cycles. Figure 6.4-1 shows the operation clock for CPU intermittent operation
mode.
Peripheral clock
CPU clock
144
Figure 6.4-1 Clock for the CPU Intermittent Operation Mode
FUJITSU MICROELECTRONICS LIMITED
Suspended cycle
Internal bus activation
MB90335 Series
1 instruction
execution cycle
CM44-10137-6E
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