7477 datasheet(190/354 Pages) RENESAS

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

HARDWARE

1.18 State transitions

Notes 1: When changing from the stop mode to another mode, oscillation stabilizing wait time is generated

automatically by connecting timer 3 and timer 4.

2: In the 7471/7478 group, where oscillating the stopped clock and switching the system clock, it

is necessary to wait at software until oscillation is stabilized. At this time, set the bit 5 of the CPU

mode register to “1” and set the XCOUT drive capacity to the high power mode. After the oscil-

lation of sub-clock f(XCIN) becomes stable, clear the bit to “0” (low power mode) as required.

3: In the 7471/7478 group, when returning from the low-speed mode to the ordinary mode, use the

main clock f(XIN) as a count source of the internal clock

φ (state B). After that, clear bit 4 of the

CPU mode register to “0” to stop the oscillation of f(XCIN) if necessary.

4: When using the low-speed mode in the 7471/7478 group, use it in one of the following states.

q Fix the XCOUT drive capacity to the high power mode (set the XCOUT drive capacity selection bit

of the CPU register to “1.”)

q When fixing the XCOUT drive capacity to the low power mode (clear the XCOUT drive capacity

selection bit of the CPU mode register to “0”), lower the value of the resistor Rd+ in the sub-

clock oscillation circuit to a level at which the oscillation of f(XCIN) does not stop.

+ “Resistor Rd”: Refer to the circuit example in “Chapter 2 Application, 2.7 Oscillation circuit.”

7477 Datasheet(PDF) 190 Page - Renesas Technology Corp