7540 datasheet(308/366 Pages) RENESAS

308 / 366 page

3-86

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

APPENDIX

7540 Group

3.3 Notes on use

3.3.13 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

↓

NOP (one or more instructions)

↓

Clear an interrupt request bit to “0”

(no interrupt request issued)

↓

Set the interrupt enable bit to “1” (interrupt enabled)

(2) 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.

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.

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. 3.3.6 Sequence of check of interrupt request bit

Fig. 3.3.5 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.

7540 Datasheet(PDF) 308 Page - Renesas Technology Corp