MC68HC08AB16A Datasheet, PDF (107/380 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
System Integration Module (SIM)
Reset and System Initialization
IRST
RST
CGMXCLK
IAB
RST PULLED LOW BY MCU
32 CYCLES
32 CYCLES
Figure 8-5. Internal Reset Timing
VECTOR HIGH
The COP reset is asynchronous to the bus clock.
ILLEGAL ADDRESS RST
ILLEGAL OPCODE RST
COPRST
LVI
POR
INTERNAL RESET
Figure 8-6. Sources of Internal Reset
The active reset feature allows the part to issue a reset to peripherals
and other chips within a system built around the MCU.
8.4.2.1 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. 64 CGMXCLK cycles later, the CPU and
memories are released from reset to allow the reset vector sequence to
occur.
At power-on, the following 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 the oscillator to stabilize
MC68HC08AB16A — Rev. 2.0
MOTOROLA
System Integration Module (SIM)
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Technical Data
107