Cpu Intermittent Operation Mode; Fig. 5.4 Clock In Cpu Intermittent Operation Mode - Fujitsu MB90420/5 (A) Series Hardware Manual

MB90420/5 (A) SERIES F

5.4 CPU Intermittent Operation Mode

In the CPU intermittent operation mode, the CPU performs the intermittent operation with the external bus
and the resources operating fast to reduce power consumption.
n CPU Intermittent operation mode
The CPU intermittent operation mode stops the clock to be supplied to the CPU for a certain period of time at
every instruction execution when accessing registers, internal memory (ROM, RAM), I/O, resources and
external buses and delays the start of the internal bus cycle. The CPU execution speed can be slowed with
high-speed resource clocks supplied to the resources to process with lower-power consumption.
• The CG1 and CG0 bits of the low-power consumption mode control register (LPMCR: CG1, CG0) are
used to select the suspended clock count to be supplied to the CPU.
• The same clock as the one supplied to the resource is used at external bus operation.
• The instruction execution time when the CPU intermittent operation mode is used can be calculated by
adding the compensation value which the instruction execution count of accesses to registers, internal
memory, internal resources and external bus is multiplied by the suspended clock cycle count, to the
normal execution time. Figure 5.4 shows the operating clock in the CPU intermittent operation mode.
RST pin
Timer mode
PLL clock
Sub-clock
CPU clock
2
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Oscillation stabilization wait
Stopped
Cancellation of timer mode

Fig. 5.4 Clock in CPU Intermittent Operation Mode

Oscillating
Stopped
Oscillating
Main clock
Reset sequence
Cancellation of reset
5-10
Processing