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• The PC is loaded from the reset exception handling vector address (H'0000 to H'0001), after
which the program starts executing from the address indicated in PC.
When system power is turned on or off, the RES pin should be held low.
Figure 3.1 shows the reset sequence.
RES
ø
Internal
address bus
Internal read
signal
Internal write
signal
Internal data
bus (16-bit)
(1) Reset exception handling vector address (H'0000)
(2) Program start address
(3) First instruction of program
3.2.3
Interrupt Immediately after Reset
After a reset, if an interrupt were to be accepted before the stack pointer (SP: R7) was initialized,
PC and CCR would not be pushed onto the stack correctly, resulting in program runaway. To
prevent this, immediately after reset exception handling all interrupts are masked. For this reason,
the initial program instruction is always executed immediately after a reset. This instruction should
initialize the stack pointer (e.g. MOV.W #xx: 16, SP).
58
Reset cleared
Vector fetch
Figure 3.1 Reset Sequence
Program initial
instruction prefetch
Internal
processing
(1)
(2)
(2)
(3)
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