Switching Cpu Clock - NEC mPD780852 Series Preliminary User's Manual

5.6.2 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 a lapse of time long enough for the V
its maximum speed, rewrite the contents of the processor clock control register (PCC) to execute the
maximum-speed operation.
CHAPTER 5 CLOCK GENERATOR
Figure 5-6. 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 to rise to the level at which the CPU can operate at
DD
Preliminary User's Manual U14581EJ3V0UM00
Fastest
operation
99