M16C26 Datasheet, PDF (18/239 Pages) Renesas Technology Corp – 16-BIT CMOS SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/20 SERIES

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Preliminary Specifications Rev. 0.9
Specifications in this manual are tentative and subject to change.
Reset
M16C/26 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Reset
There are two types of reset: a hardware reset and a software reset (See “Software Reset” for details on
software resets.)
Hardware reset
There are two kinds of hardware reset: hardware reset 1 and hardware reset 2.
Hardware reset 1
A reset is applied using the RESET pin. When a low-level signal (“L”) is applied to the RESET pin,
while the power supply voltage is within the recommended operating voltage, the pins are initialized
(see Table 1.5.1). When the input level of the RESET pin is released from low to high, the CPU and
SFR are initialized. The program is executed starting from the address indicated by the reset vector.
The internal RAM is not initialized. If the RESET pin is pulled low while writing to the internal RAM, the
internal RAM becomes indeterminate.
Figure 1.5.1 shows an example of the reset circuit. Table 1.5.1 shows the status of the other pins while
the RESET pin is “L”. Figure 1.5.2 shows the reset sequence. Figure 1.5.3 shows the status of the
CPU registers. Refer to the SFR section on the status of SFR registers after reset.
1. When the power supply is stable (warm start)
(1) Apply a low-level signal to the RESET pin
(2) Supply at least 20 clock cycles to the XIN pin
(3) Apply a high-level signal to the RESET pin
2. Power on (cold start)
(1) Apply a low-level signal to the RESET pin
(2) Turn on or increase the power supply voltage until it meets the recommended operation
voltage.
(3) Wait at least 2ms for the power supply to stabilize
(4) Supply at least 20 clock cycles to the XIN pin
(5) Apply a high-level signal to the RESET pin
Hardware reset 2
This reset is generated by the microcomputer's internal voltage detection circuit. The voltage detec-
tion circuit monitors the voltage supplied to the VCC pin. A reset is generated when the VCC input
voltage drops to VDET3 or less while VCR2 register's VC26 bit is equal to “1” (VDET3 detection circuit
enabled). When the input voltage increases so it is greater than VDET3, the CPU, SFR, and pins are
initialized, and the program is executed starting from the address indicated by the reset vector. After
VDET3 is detected, it takes about 2ms before the program is executed. The status of the pins and
registers after the reset is similar to that of hardware reset 1.
Take note, however, that the value of VC26 has no effect in stop mode. Therefore, a reset is not
applied even if the VCC input voltage drops to VDET3 or lower.
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