HD6433694 Datasheet, PDF (85/432 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series

3. The CPU accepts the NMI and address break without depending on the I bit value. Other
interrupt requests are accepted, if the I bit is cleared to 0 in CCR; if the I bit is set to 1, the
interrupt request is held pending.
4. If the CPU accepts the interrupt after processing of the current instruction is completed,
interrupt exception handling will begin. First, both PC and CCR are pushed onto the stack. The
state of the stack at this time is shown in figure 3.2. The PC value pushed onto the stack is the
address of the first instruction to be executed upon return from interrupt handling.
5. Then, the I bit of CCR is set to 1, masking further interrupts excluding the NMI and address
break. Upon return from interrupt handling, the values of I bit and other bits in CCR will be
restored and returned to the values prior to the start of interrupt exception handling.
6. Next, the CPU generates the vector address corresponding to the accepted interrupt, and
transfers the address to PC as a start address of the interrupt handling-routine. Then a program
starts executing from the address indicated in PC.
Figure 3.3 shows a typical interrupt sequence where the program area is in the on-chip ROM and
the stack area is in the on-chip RAM.
SP – 4
SP – 3
SP – 2
SP – 1
SP (R7)
Stack area
SP (R7)
SP + 1
SP + 2
SP + 3
SP + 4
CCR
CCR^*3
PCH
PCL
Even address
Prior to start of interrupt
exception handling
PC and CCR
saved to stack
Legend:
PCH : Upper 8 bits of program counter (PC)
PCL : Lower 8 bits of program counter (PC)
CCR: Condition code register
SP: Stack pointer
After completion of interrupt
exception handling
Notes: 1. PC shows the address of the first instruction to be executed upon return from the interrupt
handling routine.
2. Register contents must always be saved and restored by word length, starting from
an even-numbered address.
3. Ignored when returning from the interrupt handling routine.
Figure 3.2 Stack Status after Exception Handling
Rev. 4.00, 03/04, page 57 of 400