Interrupts After Reset - Hitachi H8S/2646 Hardware Manual

Ø
RES
Address bus
RD
HWR, LWR
D15 to D0
(1) (3) Reset exception handling vector address (when reset, (1) = H'000000,
(3) = H'000002)
(2) (4) Start address (contents of reset exception handling vector address)
(5) Start address ((5) = (2) (4))
(6) First program instruction
Note: * 3 program wait states are inserted.
4.2.3

Interrupts after Reset

If an interrupt is accepted after a reset but before the stack pointer (SP) is initialized, the 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. Since the first instruction of a program is
always executed immediately after the reset state ends, make sure that this instruction initializes
the stack pointer (example: MOV.L #xx: 32, SP).
94
*
(1)
(2)
Figure 4-3 Reset Sequence (Mode 4)
Vector Internal
fetch processing
*
(3)
High
(4)
Prefetch of first program
instruction
*
(5)
(6)