7477 datasheet(175/354 Pages) RENESAS

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7470/7471/7477/7478 GROUP USER’S MANUAL

1-158

HARDWARE

1.16 Oscillation circuit

1.16.4 Oscillation stabilizing time

In the oscillation circuit using a ceramic resonator or a crystal oscillator, the oscillation becomes unstable

for a certain period at a start of oscillation of the oscillator. The time required for stabilization of oscillation

is called oscillation stabilizing time.

A proper oscillation stabilizing wait time fit for the used oscillation circuit is required. For the oscillation

stabilizing time, ask the oscillator maker for information.

(1) Oscillation stabilizing wait time at power on

In the 7470/7471/7477/7478 group, the oscillation stabilizing wait time for 32768 counts of the XIN

pin input signal is automatically generated in the period from power on to reset release.

Figure 1.16.2 shows a oscillation stabilizing wait time after power on.

(2) Oscillation stabilizing wait time at recovery from stop mode

In the stop mode, oscillation stops. When the previous mode is restored from the stop mode by

inputting a reset signal or generating an interrupt, the oscillation stabilizing wait time for 32768

counts of the XIN pin input signal or the XCIN pin input signal is automatically generated in the same

way as the power on time.

q At recovery by reset, f(XIN) becomes a count source that generates oscillation stabilizing wait time.

q At recovery by interrupt, the count source of timer 3 set immediately before execution of the STP

instruction becomes a count source that generates oscillation stabilizing wait time. Note that when

f(XIN) is the system clock, the oscillation of the f(XCIN) side may not be stabilized after the lapse

of this oscillation stabilizing wait time.

For the details of the stop mode, refer to “1.17.1 Stop mode.”

Note: In the 7470/7477 group, f(XCIN) is not available.

Fig. 1.16.2 Oscillation stabilizing wait time after power on

XIN

VCC

RESET

µs or more

Internal reset

Release internal reset state

2.7V

V : At f(XIN) = (2.2 VCC – 2) MHz

Oscillation stabilizing wait time

32768 counts of X IN pin input signal

7477 Datasheet(PDF) 175 Page - Renesas Technology Corp