Datasheet

MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor 47
Chapter 4
Configuration Register (CONFIG)
4.1 Introduction
This section describes the configuration registers, CONFIG1 and CONFIG2. The configuration registers
control these options:
• Stop mode recovery time, 32 CGMXCLK cycles or 4096 CGMXCLK cycles
• Computer operating properly (COP) timeout period, 2
18
–2
4
or 2
13
–2
4
CGMXCLK cycles
•STOP instruction
• Computer operating properly (COP) module
• Low-voltage inhibit (LVI) module control and voltage trip point selection
• Enable/disable the oscillator (OSC) during stop mode
• Serial communications interface (SCI) clock source selection
• External clock/crystal source control
• Enable/disable for the FLASH charge-pump regulator
4.2 Functional Description
The configuration registers are used in the initialization of various options and can be written once after
each reset. All of the configuration register bits are cleared during reset. Since the various options affect
the operation of the microcontroller unit (MCU), it is recommended that these registers be written
immediately after reset. The configuration registers are located at $001E and $001F. For compatibility, a
write to a read-only memory (ROM) version of the MCU at this location will have no effect. The
configuration register may be read at anytime.
NOTE
The CONFIG module is known as an MOR (mask option register) on a
ROM device. On a ROM device, the options are fixed at the time of device
fabrication and are neither writable nor changeable by the user.
On a FLASH device, the CONFIG registers are special registers containing
one-time writable latches after each reset. Upon a reset, the CONFIG
registers default to predetermined settings as shown in Figure 4-1 and
Figure 4-2.
Address: $001E
Bit 7654321Bit 0
Read:
R
0
EXT-
XTALEN
EXT-
SLOW
EXT-
CLKEN
0
OSCENIN-
STOP
SCIBD-
SRC
Write:
Reset:00000000
= Unimplemented R = Reserved
Figure 4-1. Configuration Register 2 (CONFIG2)