
7540 Group User
’
s Manual
APPLICATION
2-137
2.9 Oscillation control
2.9.3 Application example of ring oscillator
The ring oscillator is the oscillation circuit which is equipped with the 7540 Group. External circuits can be
eliminated by using this oscillator as the operation clock or by using this oscillator with a ceramic or RC
oscillation circuit. When this oscillator is used as the operation clock, all peripheral functions can be used.
In this section, the setting method and application example are explained.
Note:
The 7540 Group starts operation by the ring oscillator.
(1) Setting method
Figure 2.9.5 shows the setting method when the ring oscillator is used as the operation clock.
Fig. 2.9.5 Setting method when the ring oscillator is used as the operation clock
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CPU mode register (CPUM) [Address 3B
16
]
CPU mode register (CPUM) [Address 3B
16
]
(2) Example of control procedure
Outline:
The frequency of the ring oscillator is measured, and an error by the power source voltage
or temperature is confirmed.
Specifications
:
The f(X
IN
) = 4 MHz is divided by timer Z and 10 ms is detected. The ring oscillator
is divided by timer Y.
The count value of timer Y is read out in the timer Z interrupt processing routine
which occurs every 10 ms, and an error from f(X
IN
) is confirmed.
Figure 2.9.6 shows an example of control procedure.