MC68HC705P9 Datasheet, PDF (66/160 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Resets and Interrupts
5.2 Resets
A reset immediately stops the operation of the instruction being
executed, initializes certain control bits, and loads the program counter
with a user-defined reset vector address. The following sources can
generate resets:
• Power-on reset (POR) circuit
• RESET pin
• COP watchdog
V_DD
RESET
POWER-ON RESET
COP WATCHDOG
(PROGRAMMABLE OPTION)
INTERNAL CLOCK
D ^S Q ^RST
CK
RESET
LATCH
TO CPU AND
SUBSYSTEMS
Figure 5-1. Reset Sources
5.2.1 Power-On Reset
NOTE:
A positive transition on the V_DD pin generates a power-on reset.
The power-on reset is strictly for power-up conditions and cannot be
used to detect drops in power supply voltage.
A 4064 t_CYC (internal clock cycle) delay after the oscillator becomes
active allows the clock generator to stabilize. If the RESET pin is at logic
zero at the end of 4064 t_CYC, the MCU remains in the reset condition until
the signal on the RESET pin goes to logic one.
Technical Data
66
Resets and Interrupts
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MC68HC705P9 — Rev. 4.0
MOTOROLA