August 27, 1998
GENERAL RELEASE SPECIFICATION
SECTION 5
RESETS
This section describes the five reset sources and how they initialize the 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 vec-
tor address. The following conditions produce a reset:
•
•
•
•
•
Initial power up of device (power on reset).
A logic zero applied to the RESET pin (external reset).
Timeout of the 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.
MCU INTERNAL REGISTER
COP WATCHDOG
LOW VOLTAGE RESET
V
POWER-ON RESET
DD
ILLEGAL ADDRESS RESET
V
DD
INTERNAL
ADDRESS BUS
100KΩ
S
TO CPU
RST
RESET
D
AND
RESET
LATCH
SUBSYSTEMS
R
3-CYCLE
CLOCKED
ONE-SHOT
INTERNAL
CLOCK
Figure 5-1. Reset Sources
MC68HC05SB7
REV 2.1
RESETS
MOTOROLA
5-1
FREESCALE [ Freescale ]
