4.3.6 Interrupt Response Time
Table 4-4 indicates the number of states that elapse from an interrupt request signal until the first
instruction of the software interrupt-handling routine is executed. Since the H8/329 Series accesses
its on-chip memory 16 bits at a time, very fast interrupt service can be obtained by placing
interrupt-handling routines in on-chip ROM and the stack in on-chip RAM.
Table 4-4. Number of States before Interrupt Service
Number of states
No.
Reason for wait
On-chip memory
External memory
1
Interrupt priority decision
2
*3
2
*3
2
Wait for completion of
1 to 13
5 to 17
*2
current instruction
*1
3
Save PC and CCR
4
12
*2
4
Fetch vector
2
6
*2
5
Fetch instruction
4
12
*2
6
Internal processing
4
4
Total
17 to 29
41 to 53
*2
Notes: *1 These values do not apply if the current instruction is EEPMOV.
*2 If wait states are inserted in external memory access, add the number of wait states.
*3 1 for internal interrupts.
4.3.7 Precaution
Note that the following type of contention can occur in interrupt handling.
Contention between Interrupt Request and Disable: When software clears the enable bit of an
interrupt to “0” to disable the interrupt, the interrupt becomes disabled after execution of the
clearing instruction. If an enable bit is cleared by a BCLR or MOV instruction, for example, and
the interrupt is requested during execution of that instruction, at the instant when the instruction
ends the interrupt is still enabled, so after execution of the instruction, the hardware exception-
handling sequence is executed for the interrupt. If a higher-priority interrupt is requested at the
same time, however, the hardware exception-handling sequence is executed for the higher-priority
interrupt and the interrupt that was disabled is ignored.
Similar considerations apply when an interrupt request flag is cleared to “0.”
72
Summary of Contents for H8/326 Series
Page 67: ...58 ...
Page 121: ...112 ...
Page 274: ... 3 Clock Settling Timing Ø VCC RES STBY tOSC1 tOSC1 Figure 14 8 Clock Setting Timing 265 ...
Page 279: ...270 ...