MC68HC08AS32 Datasheet, PDF (131/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

System Integration Module (SIM)
SIM Counter
9.5 SIM Counter
The SIM counter is used by the power-on reset module (POR) and in
stop mode recovery to allow the oscillator time to stabilize before
enabling the internal bus (IBUS) clocks. The SIM counter also serves as
a prescaler for the computer operating properly (COP) module. The SIM
counter overflow supplies the clock for the COP module. The SIM
counter is 12 bits long and is clocked by the falling edge of CGMXCLK.
9.5.1 SIM Counter During Power-On Reset
The power-on reset module (POR) detects power applied to the MCU.
At power-on, the POR circuit asserts the signal PORRST. Once the SIM
is initialized, it enables the clock generation module (CGM) to drive the
bus clock state machine.
9.5.2 SIM Counter During Stop Mode Recovery
The SIM counter also is used for stop mode recovery. The STOP
instruction clears the SIM counter. After an interrupt, break, or reset, the
SIM senses the state of the short stop recovery bit, SSREC, in the MOR
register. If the SSREC bit is a logic 1, then the stop recovery is reduced
from the normal delay of 4096 CGMXCLK cycles down to 32 CGMXCLK
cycles. This is ideal for applications using canned oscillators that do not
require long startup times from stop mode. External crystal applications
should use the full stop recovery time with SSREC cleared.
9.5.3 SIM Counter and Reset States
External reset has no effect on the SIM counter. (See 9.7.2 Stop Mode
for details.) The SIM counter is free-running after all reset states. (See
9.4.2 Active Resets from Internal Sources for counter control and
internal reset recovery sequences.)
MC68HC08AS32 — Rev. 3.0
MOTOROLA
System Integration Module (SIM)
Advance Information
131