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8.4.2.1 Power-On Reset
MC68HC908AB32
Rev. 1.0
—
MOTOROLA
IRST
RST PULLED LOW BY MCU
RST
CGMXCLK
IAB
Figure 8-5. Internal reset timing
The COP reset is asynchronous to the bus clock.
ILLEGAL ADDRESS RST
ILLEGAL OPCODE RST
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.
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
System Integration Module (SIM)
System Integration Module (SIM)
Reset and System Initialization
32 CYCLES
32 CYCLES
COPRST
INTERNAL RESET
LVI
POR
VECTOR HIGH
Technical Data
115
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