MC68HC908RF2 Datasheet, PDF (89/254 Pages) Motorola, Inc – HCMOS Microcontroller Unit

System Integration Module (SIM)
Reset and System Initialization
6.4.2.1 Power-On Reset
When power is first applied to the MCU, the power-on reset module
(POR) generates a pulse to indicate that power-on has occurred. The
external reset pin (RST) is held low while the SIM counter counts out
4096 CGMXCLK cycles. Another 64 CGMXCLK cycles later, the CPU
and memories are released from reset to allow the reset vector
sequence to occur.
At power-on, these events occur:
• A POR pulse is generated.
• The internal reset signal is asserted.
• The SIM enables CGMOUT.
• Internal clocks to the CPU and modules are held inactive for 4096
CGMXCLK cycles to allow stabilization of the oscillator.
• The RST pin is driven low during the oscillator stabilization time.
• The POR bit of the SIM reset status register (SRSR) is set and all
other bits in the register are cleared.
OSC1
PORRST
CGMXCLK
CGMOUT
RST
IAB
4096
CYCLES
32
CYCLES
32
CYCLES
$FFFE
$FFFF
Figure 6-7. POR Recovery
MC68HC908RF2 — Rev. 1
MOTOROLA
System Integration Module (SIM)
Advance Information
89