INTERRUPTS
[Precautions for interrupts]
[Precautions for interrupts]
1. In order to change the interrupt priority level select bits (bits 0 to 2 at addresses 6E16 to 7C16, F516 to F916
,
FD16 to FF16), 2 to 7 cycles of fsys are required after execution of a write instruction until change of the
interrupt priority level. Therefore, when the interrupt priority level of a certain interrupt source is repeatedly
changed in a very short time, which consists of a few instructions, it is necessary to reserve the time
required for the change by software. Figure 6.10.7 shows a program example to reserve the time required
for the change. Note that the time required for the change depends on the contents of the interrupt priority
detection time select bits (bits 4 and 5 at address 5E16). Table 6.10.2 lists the correspondence between
the number of instructions inserted in Figure 6.10.7 and the interrupt priority detection time select bits.
:
; Write instruction for the interrupt priority level select bits
MOVMB 00XXH, #0XH
; Inserted NOP instruction (Note)
NOP
;
NOP
;
NOP
; Write instruction for the interrupt priority level select bits
MOVMB 00XXH, #0XH
:
Note: Except a write instruction for address XX16, any instruction which has the same
cycles as the NOP instruction can also be inserted, instead of the NOP instruction.
For the number of inserted NOP instructions, see Table 6.10.2.
XX: any of 6E to 7F, F1, F2, F5 to F9, and FD to FF
Fig. 6.10.7 Program example to reserve time required for change of interrupt priority level
Table 6.10.2 Correspondence between number of instructions to be inserted in Figure 6.10.7 and
interrupt priority detection time select bits
Interrupt priority level
detection time
Number of inserted
NOP instructions
7 or more
Interrupt priority detection time select bits (Note)
b5
0
b4
0
7 cycles of fsys
0
1
4 cycles of fsys
2 cycles of fsys
Do not select.
4 or more
1
0
2 or more
1
1
Note: We recommend [b5 = “1”, b4 = “0”].
2. When allocating pin INT
0 (output disabled).
3
to pin P7
4
, be sure that the D-A
1
output enable bit (bit 2 at address 9616) =
3. When using pin P6OUTCUT/INT
4
as an input pin of an external interrupt (pin INT ), be sure to use port pins
4
P6
0
to P6
5
in the input mode. (Refer to section “5.2.3 Pin P6OUTCUT/INT .”)
4
7906 Group User’s Manual Rev.2.0
6-23
RENESAS [ RENESAS TECHNOLOGY CORP ]
