R8C/13 Group
5.1 Hardware Reset
5.1.3 Power-on Reset Function
The power-on reset is the function which can reset the microcomputer without the external reset
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circuit. The RESET pin should be connected to the VCC pin via about 5 kΩ pull-up resistance using
the power-on reset function, the function turns to active and the microcomputer has its pins, CPU,
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and SFR initialized. When a capacitor is connected to the RESET pin, always keep the voltage to the
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RESET pin 0.8 VCC or more.
When the input voltage at the VCC pin reaches to the Vdet level, count operation of the low-speed on-
chip oscillator clock starts. When the operation counts the low-speed on-chip oscillator clock for 32
times, the internal reset is released. Then the program is executed starting from the address indi-
cated by the reset vector. The initialized pins and registers and the status thereof are the same as in
hardware reset 1 excluding the following bits.
• The D40 bit in the D4INT register turns to “1” automatically (voltage detection interrupt enabled)
• The D46 bit in the D4INT register turns to “1” automatically (hardware reset 2 when going through
Vdet)
Additionally, the hardware reset 2 turns to active after the power-on reset. This is because the VC27
bit in the VCR2 register is set to “1” (voltage detection circuit enabled) after the power-on reset same
as the hardware reset 1, so that hardware reset 2 active conditions are all satisfied including above
D40 and D46 bit conditions.
Figure 5.5 shows the power-on reset circuit. Figure 5.6 shows the power-on reset operation.
Internal reset signal
RESET
Q
S
R
5-bit
counter
fRING-S
Trigger
VCC ≥ Vdet detection
Figure 5.5 Power-on Reset Circuit
Rev.1.20 Jan 27, 2006 page 18 of 205
REJ09B0111-0120
RENESAS [ RENESAS TECHNOLOGY CORP ]
