UPD78320 datasheet(49/88 Pages) NEC

49 / 88 page

µPD78320, 78322

OPERATION AFTER RESET

If the RESET input pin is set to the low level, the system reset is applied and each hardware becomes as initialized status

(reset status). If RESET input becomes high level, the reset state is released and program execution is started. Initialize

the contents of various registers in the program as required.

Change the number of cycles for the programmable wait control register and the fetch cycle control register as required

in particular.

The RESET input pin is equipped with an analog delay noise eliminator to prevent malfunctioning due to noise.

Cautions 1. While RESET is active (low level), all pins remain high impedance (except WDTO, AVREF, AVDD, AVSS,

VDD, VSS, X1 and X2).

2. If RAM has been expanded externally, mount a pull-up resistor to the P90/RD and P91/WR pins. It is

possible that the P90/RD and P91/WR pins become high impedance resulting in an external RAM

contents corruption. In addition, signals may collide on the address/data bus, resulting in the

destruction of the input/output circuit.

Figure 7-1. Reset Signal Acknowledge

For reset operation upon power-up, secure the oscillation stabilization time of about 40 msec from power-up to reset

acknowledge as shown in Figure 7-2.

Figure 7-2. Reset Upon Power-Up

RESET Input

Analog

Delay

Eliminated

as Noise

Analog

Delay

Reset

Acknowl-

edged

Analog

Delay

Reset

Release

Oscillation

Stabilization

Time

Analog

Delay

Reset

Release

VDD

RESET

UPD78320 Datasheet(PDF) 49 Page - NEC