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φ
RES
Internal
address bus
Internal
read signal
Internal
write signal
Internal
data bus
(16 bits wide)
(1) Address of reset exception handling vector (H'0000)
(2) Start address (contents of reset exception handling vector address)
(3) First instruction of program
4.2.3
Interrupts after Reset
If an interrupt is accepted after a reset but before the stack pointer (SP) is initialized, PC and CCR
will not be saved correctly, leading to a program crash. To prevent this, all interrupt requests,
including NMI, are disabled immediately after a reset exception handling. The first instruction of
the program is always executed immediately after the reset state ends. This instruction should
initialize the stack pointer (example: MOV.L #xx:32, SP).
Vector fetch
(1)
(2)
Figure 4.4 Reset Sequence (Mode 6)
Prefetch of
Internal
first program
processing
instruction
(2)
(3)
89
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