User’s Manual U13850EJ4V0UM
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CHAPTER 15 RESET FUNCTION
15.1 General
When a low-level input occurs at the RESET pin, a system reset is performed and the various on-chip hardware
devices are reset to their initial settings. In addition, oscillation of the main clock is stopped during the reset period,
although oscillation of the sub clock continues.
When the input at the RESET pin changes from low level to high level, the reset status is canceled and the CPU
resumes program execution. The contents of the various registers should be initialized within the program as
necessary.
An on-chip noise eliminator uses analog delay to prevent noise-related malfunction of the RESET pin.
15.2 Pin Operations
During the system reset period, high impedance is set at almost all pins (all pins except for RESET, X2, XT2,
REGC, AV
REF
, V
DD
, V
SS
, AV
DD
, AV
SS
, BV
DD
, BV
SS
, EV
DD
, EV
SS
, and V
PP
/IC).
Accordingly, if connected to an external memory device, be sure to attach a pull-up (or pull-down) resistor for each
pin. If such a resistor is not attached, high impedance will be set for these pins, which could damage the data in
memory devices. Likewise, make sure the pins are handled so as to prevent such effects at the signal outputs by on-
chip peripheral I/O functions and output ports.
Figure 15-1. System Reset Timing
Analog
delay
Eliminated as noise
Hi-Z
X1
Analog delay
20.2 ms (@ 20 MHz operation)
RESET
Internal system
reset signal
Reset is acknowledged
Reset is canceled
Oscillation stabilization time
Analog delay