MC68HC705JP7 Datasheet, PDF (66/242 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Resets
Freescale Semiconductor, Inc.
5.2 Introduction
This section describes the five reset sources and how they initialize the
microcontroller unit (MCU). 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. These
conditions produce a reset:
• Initial power-up of device (power-on reset)
• A logic 0 applied to the RESET pin (external reset)
• Timeout of the computer operating properly (COP) watchdog
(COP reset)
• Low voltage applied to the device (LVR reset)
• Fetch of an opcode from an address not in the memory map
(illegal address reset)
Figure 5-1 shows a block diagram of the reset sources and their
interaction.
MASK OPTION REGISTER ($1FF1)
INTERNAL DATA BUS
V_DD
RESET
Advance Information
66
COP WATCHDOG
LOW-VOLTAGE RESET
POWER-ON RESET
ILLEGAL ADDRESS RESET
INTERNAL
ADDRESS BUS
3-CYCLE
CLOCKED
1-SHOT
Figure 5-1. Reset Sources
S
D
RST
RESET
LATCH
R
TO CPU
AND
SUBSYSTEMS
INTERNAL
CLOCK
MC68HC705JJ7 • MC68HC705JP7 — REV 4
Resets
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