M38B5XMXH Datasheet, PDF (262/355 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
3.3 Notes on use
3.3 Notes on use
3.3.1 Notes on interrupts
(1) 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)
Fig. 3.3.1 Sequence of switch detection edge
s Reason
The interrupt circuit recognizes the switching of the detection edge as the change of external input
signals. This may cause an unnecessary interrupt.
(2) Check of interrupt request bit
q 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.
s 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.
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
Fig. 3.3.2 Sequence of check of interrupt request bit
3-14
38B5 Group User’s Manual