RESET
3.1 Reset operation
3.1.3 Power-on reset
The following describes the operation of the microcomputer at power-on reset.
➀
After powered on, within the several ten cycles of f
sys
after the voltage level at pin Vcc meets the recommended
operating conditions with the voltage level at pin RESET = “L,” the microcomputer initializes pins; refer to
section
“3.2 Pin state.”
➁
After the voltage level at pin RESET goes from “L” to “H,” the microcomputer initializes the CPU and
SFR area within a period of 8 to 9 cycles of f
sys
. (Contents of the internal RAM area become undefined;
refer to section
“3.3 State of internal area.”)
➂
After
➁,
the microcomputer performs “Internal processing sequence after reset.”; refer to section
“3.4
Internal processing sequence after reset.”
➃
The microcomputer executes a program beginning with the address which has been set into the reset
vector addresses (addresses FFFE
16
and FFFF
16
).
Figure 3.1.3 shows the power-on reset conditions.
Figure 3.1.4 shows an example of a power-on reset
circuit.
After the voltage level at pin Vcc meets the
recommended operating conditions and the oscillator’s
operation is stabilized (see Figure 3.1.3.), apply “L”
level of voltage to pin RESET for 10
µs
or more.
When an oscillator is used, the time required for
stabilizing oscillation depends on the oscillator. For
details, contact the oscillator manufacturer.
V
CC
level
V
CC
0V
RESET
0V
0.2 V
CC
level
10
µs
X
IN
0V
Powered on there
Oscillation stabilized
Fig. 3.1.3 Power-on reset conditions
5V
M37906
1 M51957AL
27 k
Ω
2
IN
V
CC
V
CC
OUT
5
RESET
47
Ω
V
SS
C
d
SW
10 kΩ
4
Delay
capacity
GND
3
�½
The delay time is about 11 ms when C
d
= 0.033
µF.
t
d
≈
0.34
✕
C
d
[µs], C
d
: [pF]
GND
Fig. 3.1.4 Example of power-on reset circuit
3-4
7906 Group User’s Manual Rev.2.0
RENESAS [ RENESAS TECHNOLOGY CORP ]
