Datasheet

Section 4 Exception Handling
Page 102 of 1408 R01UH0309EJ0500 Rev. 5.00
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
RES
RD
HWR, LWR
D15 to D0
High
* * *
φ
Address bus
Vector fetch
Internal
processing
Prefetch of first
program instruction
(1)
(2) (4) (6)
(3) (5)
(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: * Seven program wait states are inserted.
Figure 4.2 Reset Sequence (Advanced Mode with On-chip ROM Disabled)
4.3.2 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).
4.3.3 On-Chip Peripheral Functions after Reset Release
After reset release, MSTPCR is initialized to H'0FFF, EXMSTPCR is initialized to H'FFFF, and
all modules except the DMAC, EXDMAC, and DTC enter the module stop state.
Consequently, on-chip peripheral module registers cannot be read or written to. Register reading
and writing is enabled when the module stop state is exited.