MC68HC908RK2 Datasheet, PDF (109/232 Pages) Motorola, Inc – Microcontroller Unit

Internal Clock Generator Module (ICG)
Functional Description
• Frequency adjust (trim) register to improve variability to ±2 percent
• Bus clock software selectable from either internal or external clock
• Clock monitor for both internal and external clocks
8.4 Functional Description
The ICG, shown in Figure 8-1, contains these major submodules:
• Clock enable circuit
• Internal clock generator
• External clock generator
• Clock monitor circuit
• Clock selection circuit
8.4.1 Clock Enable Circuit
The clock enable circuit is used to enable the internal clock (ICLK) or
external clock (ECLK). The clock enable circuit generates an ICG stop
(ICGSTOP) signal which stops all clocks (ICLK, ECLK, and the low-
frequency base clock, IBASE) low. ICGSTOP is set and the ICG is
disabled in stop mode.
The internal clock enable signal (ICGEN) turns on the internal clock
generator which generates ICLK. ICGEN is set (active) whenever the
ICGON bit is set and the ICGSTOP signal is clear. When ICGEN is clear,
ICLK and IBASE are both low.
The external clock enable signal (ECGEN) turns on the external clock
generator which generates ECLK. ECGEN is set (active) whenever the
ECGON bit is set and the ICGSTOP signal is clear. When ECGEN is
clear, ECLK is low.
MC68HC908RK2 — Rev. 4.0
MOTOROLA
Internal Clock Generator Module (ICG)
Advance Information
109