
7531 Group User’s Manual
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APPENDIX
3.3 Notes on use
3.3.1 Notes on interrupts
(1) Setting of interrupt request bit and interrupt enable bit
To set an interrupt request bit and an interrupt enable bit for interrupts, execute as the following
sequence :
Clear an interrupt request bit to “0” (no interrupt request issued).
Set an interrupt enable bit to “1” (interrupts enabled).
q Reason
If the above setting , are performed simultaneously with one instruction, an unnecessary
interrupt processing routine is executed. Because an interrupt enable bit is set to “1” (interrupts
enabled) before an interrupt request bit is cleared to “0”.
(2) Switching external interrupt detection edge
For the products able to switch the external interrupt detection edge, switch it as the following
sequence.
Clear an interrupt enable bit to “0” (interrupt disabled)
↓
Switch the detection edge
↓
Clear an interrupt request bit to “0”
(no interrupt request issued)
↓
Set the interrupt enable bit to “1” (interrupt enabled)
3.3 Notes on use
Fig. 3.3.1 Sequence of switch the detection edge
q Reason
The interrupt circuit recognizes the switching of the detection edge as the change of external input
signals. This may cause an unnecessary interrupt.
(3) Check of interrupt request bit
When executing the BBC or BBS instruction to an interrupt request bit of an interrupt request register
immediately after this bit is set to “0” by using a data transfer instruction, execute one or more
instructions before executing the BBC or BBS instruction.
Clear the interrupt request bit to “0” (no interrupt issued)
↓
NOP (one or more instructions)
↓
Execute the BBC or BBS instruction
Data transfer instruction:
LDM, LDA, STA, STX, and STY instructions
q Reason
If the BBC or BBS instruction is executed
immediately after an interrupt request bit of
an interrupt request register is cleared to
“0”, the value of the interrupt request bit
before being cleared to “0” is read.
Fig. 3.3.2 Sequence of check of interrupt request bit