MC68HC908RK2 Datasheet, PDF (41/158 Pages) Motorola, Inc – Microcontroller Unit

Chapter 3
Configuration Register (CONFIG)
3.1 Introduction
This section describes the configuration register (CONFIG). The configuration register enables or
disables these options:
• Stop mode recovery time (32 CGMXCLK cycles or 4,096 CGMXCLK cycles)
• COP timeout period (2¹⁸ – 2⁴ or 2¹³ – 2⁴ CGMXCLK cycles)
• STOP instruction
• Computer operating properly module (COP)
• Low-voltage inhibit (LVI) module control
3.2 Functional Description
The CONFIG register is used in the initialization of various options and can be written once after each
reset. The register is set to the documented value during reset. Since the various options affect the
operation of the MCU, it is recommended that these registers be written immediately after reset. The
configuration register is located at $001F.
NOTE
On a FLASH device, the options are one-time writable by the user after
each reset. The CONFIG register is not in the FLASH memory but is a
special register containing one-time writable latches after each reset. Upon
a reset, the CONFIG register defaults to predetermined settings as shown
in Figure 2-1. Memory Map.
Address: $001F
BIt 7
6
5
4
3
2
1
Read:
EXTSLOW
Write:
Reset:
0
LVISTOP
0
LVIRST
1
LVIPWR COPRS
1
0
SSREC
0
STOP
0
Figure 3-1. Configuration Register (CONFIG)
Bit 0
COPD
0
EXTSLOW — Slow External Crystal Enable Bit
The EXTSLOW bit has two functions. It configures the ICG module for a fast (1 MHz–8 MHz) or slow
(30 kHz–100 kHz) speed crystal. The option also configures the clock monitor operation in the ICG
module to expect an external frequency higher (307.2 kHz–32 MHz) or lower (60 Hz–307.2 kHz) than
the base frequency of the internal oscillator. See Chapter 6 Internal Clock Generator Module (ICG).
1 = ICG set for slow external crystal operation
0 = ICG set for fast external crystal operation
MC68HC908RK2 Data Sheet, Rev. 5.1
Freescale Semiconductor
41