MC68HC908AS32A Datasheet, PDF (192/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

System Integration Module (SIM)
15.2.2 Clock Startup from POR or LVI Reset
When the power-on reset module or the low-voltage inhibit module generates a reset, the clocks to the
CPU and peripherals are inactive and held in an inactive phase until after 4096 CGMXCLK cycles. The
RST pin is driven low by the SIM during this entire period. The bus clocks start upon completion of the
timeout.
15.2.3 Clocks in Stop Mode and Wait Mode
Upon exit from stop mode by an interrupt, break, or reset, the SIM allows CGMXCLK to clock the SIM
counter. The CPU and peripheral clocks do not become active until after the stop delay timeout. This
timeout is selectable as 4096 or 32 CGMXCLK cycles. See 15.6.2 Stop Mode.
In wait mode, the CPU clocks are inactive. Refer to the wait mode subsection of each module to see if the
module is active or inactive in wait mode. Some modules can be programmed to be active in wait mode.
15.3 Reset and System Initialization
The MCU has these reset sources:
• Power-on reset module (POR)
• External reset pin (RST)
• Computer operating properly module (COP)
• Low-voltage inhibit module (LVI)
• Illegal opcode
• Illegal address
All of these resets produce the vector $FFFE–FFFF ($FEFE–FEFF in monitor mode) and assert the
internal reset signal (IRST). IRST causes all registers to be returned to their default values and all
modules to be returned to their reset states.
An internal reset clears the SIM counter (see 15.4 SIM Counter), but an external reset does not. Each of
the resets sets a corresponding bit in the SIM reset status register (SRSR) (see 15.7 SIM Registers).
15.3.1 External Pin Reset
Pulling the asynchronous RST pin low halts all processing. The PIN bit of the SIM reset status register
(SRSR) is set as long as RST is held low for at least the minimum t_RL time. Figure 15-4 shows the relative
timing.
CGMOUT
RST
IAB
PC
VECT H VECT L
Figure 15-4. External Reset Timing
MC68HC908AS32A Data Sheet, Rev. 2.0
192
Freescale Semiconductor