865
Reset
Chapter 26
Preliminary User’s Manual U17566EE1V2UM00
Note
In the table above, “Undefined” means either undefined at the time of a
power-on reset, or undefined due to data destruction when the falling edge of
the external RESET signal corrupts an ongoing RAM write access.
The internal RAM of the microcontroller comprises several separate RAM
blocks. In case writing to one RAM block while a reset occurs the contents of
only this RAM block may be corrupted. The other RAM blocks remain
unchanged.
26.1.2
Reset at power-on
The Power-On-Clear circuit (POC) permanently compares the power supply
voltage V
DD
with an internal reference voltage (V
IP
). It ensures that the
microcontroller only operates as long as the power supply exceeds a well-
defined limit.
When the power supply voltage falls below the internal reference voltage
(V
DD
< V
IP
), the internal reset signal RESPOC is generated.
After Power-On-Clear reset, the RESSTAT register is cleared and the
RESSTAT.RESPOC bit is set (RESSTAT = 01
H
, refer also to
“RESSTAT - Reset
source flag register“ on page 868
for the interaction between Power-On-Clear
and external RESET). The system reset signals SYSRES and SYSRESWDT
are generated.
Note
1.
Depending on the supply voltage drop rate it may be required to apply an
external RESET signal additionally in order to avoid microcontroller
operation out of the specified operating conditions. For detailed electrical
characteristics refer to the Electrical Target Specification.
2.
POC shares the reference voltage supply with the power regulators.
The following figure shows the timing when a reset is performed at power-on.
The Power-On-Clear function holds the microcontroller in reset state as long
as the power supply voltage does not exceed the threshold level V
IP
.
Figure 26-2
Timing of internal reset signal generation by Power-On-Clear circuit
Time
Delay
Supply voltage
(V
DD
)
Internal reference
voltage (V
IP
)
SYSRES
Reset period
Reset period
Reset period
SYSRESWDT
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