R8C/10 Group 5. Reset
Rev.1.20 Jan 27, 2006 page 14 of 180
REJ09B0019-0120
5. Reset
There are three types of resets: a hardware reset, a software reset, and an watchdog timer reset.
5.1 Hardware Reset
____________ ____________
A reset is applied using the RESET pin. When an “L” signal is applied to the RESET pin while
the power supply voltage is within the recommended operating condition, the pins are initial-
____________
ized (see Table 5.1 “Pin Status When RESET Pin Level is 'L'”). When the input level at the
____________
RESET pin is released from “L” to “H”, the CPU and SFR are initialized, and the program is
executed starting from the address indicated by the reset vector. Figure 5.1 shows the CPU
register status after reset and figure 5.2 shows the reset sequence. After reset, the on-chip
oscillator clock divided by 8 is automatically selected for the CPU. The internal RAM is not
____________
initialized. If the RESET pin is pulled “L” while writing to the internal RAM, the internal RAM
becomes indeterminate. Figures 5.3 to 5.4 show the reset circuit example. Refer to Chapter 4,
“Special Function Register (SFR)” for the status of SFR after reset.
• When the power supply is stable
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(1) Apply an “L” signal to the RESET pin.
(2) Wait for 500 µs (1/fRING ✕ 20).
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(3) Apply an “H” signal to the RESET pin.
• Power on
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(1) Apply an “L” signal to the RESET pin.
(2) Let the power supply voltage increase until it meets the recommended operating condition.
(3) Wait td(P-R) or more until the internal power supply stabilizes.
(4) Wait for 500 µs (1/fRING ✕ 20).
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(5) Apply an “H” signal to the RESET pin.
5.3 Watchdog Timer Reset
Where the PM12 bit in the PM1 register is “1” (reset when watchdog timer underflows), the microcom-
puter initializes its pins, CPU and SFR if the watchdog timer underflows. Then the program is ex-
ecuted starting from the address indicated by the reset vector. After reset, the on-chip oscillator clock
divided by 8 is automatically selected for the CPU.
____________
Table 5.1 Pin Status When RESET Pin Level is “L”
Status
CNV
SS
= V
SS
Pin name
P0
P1
P3
0
to P3
3
, P3
7
P4
5
to
P4
7
Input port
Input port
Input port
Input port
5.2 Software Reset
When the PM03 bit in the PM0 register is set to “1” (microcomputer reset), the microcomputer has its
pins, CPU, and SFR initialized. Then the program is executed starting from the address indicated by
the reset vector. After reset, the on-chip oscillator clock divided by 8 is automatically selected for the
CPU.
(11 pages)
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