MC68HC11E Motorola, MC68HC11E Datasheet - Page 89

• Manufacturer Part Number: MC68HC11E
• Description: Microcontrollers
• Manufacturer: Motorola

5.1 Introduction
5.2 Resets
5.2.1 Power-On Reset (POR)
M68HC11E Family — Rev. 5
MOTOROLA
Data Sheet — M68HC11E Family
NOTE:
Resets and interrupt operations load the program counter with a vector that points
to a new location from which instructions are to be fetched. A reset immediately
stops execution of the current instruction and forces the program counter to a
known starting address. Internal registers and control bits are initialized so the
MCU can resume executing instructions. An interrupt temporarily suspends normal
program execution while an interrupt service routine is being executed. After an
interrupt has been serviced, the main program resumes as if there had been no
interruption.
The four possible sources of reset are:
POR and RESET share the normal reset vector. COP reset and the clock monitor
reset each has its own vector.
A positive transition on V
for power-up conditions. POR cannot be used to detect drops in power supply
voltages. A 4064 t
active allows the clock generator to stabilize. If RESET is at logical 0 at the end of
4064 t
The POR circuit only initializes internal circuitry during cold starts. Refer to
Figure 1-7. External Reset
It is important to protect the MCU during power transitions. Most M68HC11
systems need an external circuit that holds the RESET pin low whenever V
below the minimum operating level. This external voltage level detector, or other
external reset circuits, are the usual source of reset in a system.
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CYC
Power-on reset (POR)
External reset (RESET)
Computer operating properly (COP) reset
Clock monitor reset
Freescale Semiconductor, Inc.
For More Information On This Product,
, the CPU remains in the reset condition until RESET goes to logical 1.
Go to: www.freescale.com
CYC
Resets and Interrupts
(internal clock cycle) delay after the oscillator becomes
DD
generates a power-on reset (POR), which is used only
Circuit.
Section 5. Resets and Interrupts
Data Sheet
DD
is
89