HD6475328CG Datasheet, PDF (124/459 Pages) Hitachi Semiconductor – Manual Gives a Hardware Description

If the data transfer enable bit is cleared to “0” (or is nonexistent), the sequence proceeds as
follows. For the case in which the data transfer controller is started, see section 6, “Data Transfer
Controller.”
5. After the CPU has finished executing the current instruction, the program counter and status
register (in minimum mode) or program counter, code page register, and status register (in
maximum mode) are saved to the stack, leaving the stack in the condition shown in figure 5-3
(a) or (b). The program counter value saved on the stack is the address of the next instruction
to be executed.
6. The T (Trace) bit of the status register is cleared to “0,” and the priority level of the interrupt is
copied to bits I2 to I0, thus masking further interrupts unless they have a higher priority level.
When an NMI is accepted, the interrupt mask level in bits I2 to I0 is set to 7.
7. The interrupt controller generates the vector address of the interrupt, and the entry at this
address in the exception vector table is read to obtain the starting address of the user-coded
interrupt handling routine.
In step 7, the same difference between the minimum and maximum modes exists as in the reset
handling sequence. In the minimum mode, one word is copied from the vector table to the
program counter, then the interrupt-handling routine starts executing from the address indicated in
the program counter. In the maximum mode, two words are read. The lower byte of the first word
is copied to the code page register. The second word is copied to the program counter. The
interrupt-handling routine starts executing from the address indicated in the code page register and
program counter.
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