
2.4.4
Reset Signal Generating Factors
Reset signals are generated by each factor as follows:
2.4.4.1
Power-on reset
The power-on reset is an internal reset that occurs when power is turned on.
During power-up, a power-on reset signal is generated while the supply voltage is below the power-on reset
release voltage. When the supply voltage rises above the power-on reset release voltage, the power-on reset
signal is released.
During power-down, a power-on reset signal is generated when the supply voltage falls below the power-
on reset detection voltage.
Refer to "Power-on Reset circuit".
2.4.4.2
External reset input (RESET pin input)
This is an external reset that is generated by the RESET pin input. Port P10 is also used as the RESET pin,
and it is configured as the RESET pin at power-up.
·
During power-up
-
When the supply voltage rises rapidly
When the power supply rise time (tVDD) is shorter than 5 [ms] with enough margin, the
reset can be released by a power-on reset or an external reset (RESET pin input).
The power-on reset logic and external reset (RESET pin input) logic are ORed. This means
that the TMP89FH42 is reset when either or both of these reset sources are asserted.
Therefore, the reset time is determined by the reset source with a longer reset period. If
the RESET pin level changes from Low to High before the supply voltage rises above the
power-on-reset release voltage (VPROFF) (or if the RESET pin level is High from the be-
ginning), the reset time depends on the power-on reset. If the RESET pin level changes from
Low to High after the supply voltage rises above VPROFF, the reset time depends on the
external reset.
In the former case, a warm-up period begins when the power-on reset signal is released.
In the latter case, a warm-up period begins when the RESET pin level becomes High. Upon
completion of the warm-up period, the CPU and peripheral circuits start operating
(Figure-
When the supply voltage rises slowly
When the power supply rise time (tVDD) is longer than 5 [ms], the reset must be released
by using the RESET pin. In this case, hold the RESET pin Low until the supply voltage rises
to the operating voltage range and oscillation is stabilized. When this state is achieved, wait
at least 5 [μs] and then pull the RESET pin High. Changing the RESET pin level to High
starts a warm-up period. Upon completion of the warm-up period, the CPU and peripheral
TMP89FH42
2. CPU Core
2.4 Reset Control Circuit
Page 44
RA004