MC68HC705JJ7 Datasheet, PDF (43/164 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 5
Resets
5.1 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
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 Advance Information Data Sheet, Rev. 4.1
Freescale Semiconductor
43