When system power is turned on or off, the RES pin should be held low.
Figure 3-1 shows the reset sequence starting from RES input.
Reset cleared
Program initial
instruction prefetch
Vector fetch
Internal
processing
RES
ø
Internal
address bus
(1)
(2)
Internal read
signal
Internal write
signal
Internal data
bus (16-bit)
(2)
(3)
(1) Reset exception handling vector address (H'0000)
(2) Program start address
(3) First instruction of program
Figure 3-1 Reset Sequence
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).
65
ETC [ ETC ]
