Exception-Handling Sequences - Renesas H8/3067 Series User Manual

Section 2 CPU
2.8.4

Exception-Handling Sequences

Reset Exception Handling: Reset exception handling has the highest priority. The reset state is
entered when the RES signal goes low. Reset exception handling starts after that, when RES
changes from low to high. When reset exception handling starts the CPU fetches a start address
from the exception vector table and starts program execution from that address. All interrupts,
including NMI, are disabled during the reset exception-handling sequence and immediately after it
ends.
Interrupt Exception Handling and Trap Instruction Exception Handling: When these
exception-handling sequences begin, the CPU references the stack pointer (ER7) and pushes the
program counter and condition code register on the stack. Next, if the UE bit in the system control
register (SYSCR) is set to 1, the CPU sets the I bit in the condition code register to 1. If the UE bit
is cleared to 0, the CPU sets both the I bit and the UI bit in the condition code register to 1. Then
the CPU fetches a start address from the exception vector table and execution branches to that
address.
Figure 2.14 shows the stack after the exception-handling sequence.
Rev. 4.00 Jan 26, 2006 page 57 of 938
REJ09B0276-0400