mc68hc05x4dw Freescale Semiconductor, Inc, mc68hc05x4dw Datasheet - Page 48

• Manufacturer Part Number: mc68hc05x4dw
• Description: Xc68hc705x4 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Power-on reset
Resets, Interrupts and Low Power Modes
MC68HC05X4
V
OSC1
Internal
processor clock
RESET
Internal
address bus
Internal
data bus
DD
t
VDDR
t
OXOV
V
DD
threshold (1-2V typical)
t
PORL
7FFE
A power-on reset occurs when a positive transition is detected on VDD.
The power-on reset function is strictly for power turn-on conditions and
should not be used to detect drops in the power supply voltage. The
power-on circuitry provides a stabilisation delay (t
oscillator becomes active. If the external RESET pin is low at the end of
this delay then the processor remains in the reset state until RESET
goes high. The user must ensure that the voltage on VDD has risen to a
point where the MCU can operate properly by the time t
If there is doubt, the external RESET pin should remain low until the
voltage on VDD has reached the specified minimum operating voltage.
This may be accomplished by connecting an external RC-circuit to this
pin to generate a power-on reset (POR). In this case, the time constant
must be great enough (at least 100 ms) to allow the oscillator circuit to
stabilise.
7FFE
Freescale Semiconductor, Inc.
Figure 1. Power-on reset and RESET
(Internal power-on reset)
Reset sequence
For More Information On This Product,
Resets, Interrupts and Low Power Modes
7FFE
7FFE
PCH
New
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t
CYC
7FFF
New
PCL
code
New
Op
PC
Program
execution
begins
t
RL
(or t
DOGL
1FFE
)
1FFE
(External hardware reset)
Reset sequence
1FFE
PORL
1FFE
PCH
New
) from when the
PORL
1FFF
New
PCL
has elapsed.
code
New
Op
Program
execution
begins
PC
2-resets