SH7144 Datasheet, PDF (94/773 Pages) Renesas Technology Corp – Hitachi SuperH RISC engine

5.1.2 Exception Processing Operations
The exception processing sources are detected and begin processing according to the timing
shown in table 5.2.
Table 5.2 Timing for Exception Source Detection and Start of Exception Processing
Exception Source
Reset
Power-on reset
Manual reset
Address error
Interrupts
Instructions Trap instruction
General illegal
instructions
Illegal slot
instructions
Timing of Source Detection and Start of Processing
Starts when the RES pin changes from low to high or when
WDT overflows.
Starts when the MRES pin changes from low to high.
Detected when instruction is decoded and starts when the
execution of the previous instruction is completed.
Starts from the execution of a TRAPA instruction.
Starts from the decoding of undefined code anytime except
after a delayed branch instruction (delay slot).
Starts from the decoding of undefined code placed in a delayed
branch instruction (delay slot) or of instructions that rewrite the
PC.
When exception processing starts, the CPU operates as follows:
1. Exception processing triggered by reset:
The initial values of the program counter (PC) and stack pointer (SP) are fetched from the
exception processing vector table (PC and SP are respectively the H'00000000 and
H'00000004 addresses for power-on resets and the H'00000008 and H'0000000C addresses for
manual resets). See section 5.1.3, Exception Processing Vector Table, for more information.
H'00000000 is then written to the vector base register (VBR) , and H'F (B'1111) is written to
the interrupt mask bits (I3 to I0) of the status register (SR). The program begins running from
the PC address fetched from the exception processing vector table.
2. Exception processing triggered by address errors, interrupts and instructions:
SR and PC are saved to the stack indicated by R15. For interrupt exception processing, the
interrupt priority level is written to the SR’s interrupt mask bits (I3 to I0). For address error
and instruction exception processing, the I3 to I0 bits are not affected. The start address is then
fetched from the exception processing vector table and the program begins running from that
address.
Rev. 2.0, 09/02, page 54 of 732