D17133CS datasheet(189/289 Pages) NEC

189 / 289 page

CHAPTER 16

RESET

174

16.3.2 Description and Operation of the Power-On Reset Function

The power-on reset function resets the microcontroller when it detects that power was turned on in the hardware,

regardless of the software state.

The power-on reset circuit operates under a lower voltage than the other internal circuits in the

µPD17120 subseries.

It initializes the microcontroller regardless whether the oscillation circuit is operating. When the reset operation is

terminated, timer counts the number of oscillation pulses sent from the oscillator until it reaches the specified value.

Within this period, oscillation becomes stable and the power voltage applied to the microcontroller enters the range

(VDD=2.7 to 5.5 V at 400 kHz to 4 MHzNote) in which the microcontroller is guaranteed to operate.

When this period elapses, the microcontroller enters normal operation mode. Figure 16-3 shows an example of

the power-on reset operation.

Note

µPD17121/17133/17P133 only

Operation of the power-on reset circuit

<1> This circuit always monitors the voltage applied to the VDD pin.

<2> This circuit resets the microcontroller Note until power reaches a particular voltage (typically 1.5 V), regardless

whether the oscillation circuit is operating.

<3> This circuit stops oscillation during the reset operation.

<4> When reset is terminated, timer counts oscillation pulses. The microcontroller waits until oscillation becomes

stable and the power voltage becomes VDD=2.7 V or higher.

Note It is from the point when the supply voltage has reached a level allowing the internal circuit to be operable

(accepting the internal reset signal) that the resetting takes effect within the microcontroller.

D17133CS Datasheet(PDF) 189 Page - NEC