CHAPTER 5. PERIPHERAL HARDWARE FUNCTIONS

As the PCC is set in 0 by RESET input, Φ is reset-started at the slowest speed (state in which the operating voltage range is wide). For this reason, in a system with a slow supply voltage rise (such as a system with a high- capacitance capacitor connected), correct operation is possible even when an adequate supply voltage cannot be attained after a power-on reset.

Fig. 5-15 Change of Φ after Power-On Reset

5V

Supply

Voltage

0V

RESET Input Signal

CPU

Operation

 

 

Progran

 

Φ￿ Change (By Program)

 

 

Start

 

 

Oscillator

 

Low-Speed

 

High-Speed

Stabilization

 

Operation

 

Operation

Time

 

 

 

 

 

Table 5-5

Maximum Time Required for Change of CPU Clock

 

 

 

 

 

PCC Before Change

PCC After Change

Max. No. of Machine Cycles

Max. Time Required for Change of

Required for Change of Φ

Φ * (When fXX = 4.19 MHz)

 

 

 

 

 

 

 

 

 

0010

 

1

 

0000

 

 

 

 

0011

 

1

 

 

 

 

 

 

 

 

 

 

0000

 

8

 

0010

 

 

 

15.3 μs

0011

 

8

 

 

 

 

 

 

 

 

 

0000

 

16

 

0011

 

 

 

 

0010

 

16

 

 

 

 

 

 

 

 

 

*When standby mode is not set until Φ changes.

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NEC PD75402A, PD75P402 user manual Change of Φ after Power-On Reset, Maximum Time Required for Change of CPU Clock