Switching Cpu Clock - NEC mPD780973 Series Preliminary User's Manual

6.6.2 Switching CPU clock

The following figure illustrates how the CPU clock switches.
V
RESET
CPU clock
<1> The CPU is reset when the RESET pin is made low on power application. The effect of resetting is released
when the RESET pin is later made high, and the main system clock starts oscillating. At this time, the time
during which oscillation stabilizes (2
After that, the CPU starts instruction execution at the slowest speed of the main system clock (3.81 µ s: at
8.38-MHz operation).
<2> After the time during which the V
speed has elapsed, PCC is rewritten so that the highest speed can be selected.
CHAPTER 6 CLOCK GENERATOR
Figure 6-6. Switching CPU Clock
DD
Slowest
operation
Wait (15.6 ms: at 8.38-MHz operation)
Internal reset operation
17
/f ) is automatically secured.
X
voltage rises to the level at which the CPU can operate at the highest
DD
Fastest
operation
97