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Section 6 Exception Handling
Page 154 of 2108 R01UH0134EJ0400 Rev. 4.00
Sep 24, 2014
SH7262 Group, SH7264 Group
6.9.5 Note before Exception Handling Begins Running
Before exception handling begins running, the exception handling vector table must be stored in a
memory, and the CPU must be able to access the memory. So, if the exception handling is
generated
Ex. 1: when the exception handling vector table is stored in an external address space, but the
settings of bus state controller and general I/O ports to access the external address space
have been not completed yet, or
Ex. 2: when the exception handling vector table is stored in the on-chip RAM, but the vector
base register (VBR) has been not changed to the on-chip RAM address yet,
the CPU fetches an unintended value as the execution start address, and starts executing programs
from unintended address.
(1) Manual Reset
Before the settings necessary to access the external CS0 space are completed, the manual reset
should not be generated. When a manual reset is issued, the CPU fetches the program execution
start address from the manual reset vector table address offset (H'00000008), which is to say
always from the external CS0 space. Additionally, in the case that no memory is connected to the
external CS0 space in boot mode 1 to 3, the manual reset should not be generated.
(2) NMI Interrupt
Before the exception handling vector table is stored in a memory and the settings necessary to
access the memory are completed, the NMI interrupt should not be generated. (Do not enable
interrupts on the 640 KB version.)
Specially in boot mode 1 to 3, the VBR is kept as the initial value H'00000000 in the period of the
boot operation (before the transfer of the loader program is completed and the CPU jumps to the
on-chip high-speed RAM). Before the VBR is changed or the settings necessary to access the
external address space are completed in the loader program, the NMI interrupt should not be
generated. (Do not enable interrupts on the 640 KB version.)
(3) Interrupts Other Than NMI
Before the exception handling vector table is stored in a memory and the settings necessary to
access the memory are completed, the settings to permit the interrupts should not be done.