MC68HC908RK2 Datasheet, PDF (106/158 Pages) Motorola, Inc – Microcontroller Unit

System Integration Module (SIM)
10.3 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 10.4 SIM Counter), but an external reset does not. Each of
the resets sets a corresponding bit in the SIM reset status register (SRSR). (See 10.7 SIM Registers.)
10.3.1 External Pin Reset
The RST pin circuit includes an internal pullup device. 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 a
minimum of 67 CGMXCLK cycles, assuming that neither the POR nor the LVI was the source of the reset.
Figure 10-4 shows the relative timing of an external reset recovery.
RST
CGMOUT
PULLED LOW EXTERNAL
PULLED HIGH EXTERNAL
IAB PC
VECT H VECT L
Figure 10-4. External Reset Recovery Timing
MC68HC908RK2 Data Sheet, Rev. 5.1
106
Freescale Semiconductor