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APPENDIX
38K0 Group User’s Manual
3.3 Notes on use
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
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.
3.3.4 Notes on timer
q If a value n (between 0 and 255) is written to a timer latch, the frequency division ratio is 1/(n+1).
q When switching the count source by the timer 12 and X count source selection bits, the value of
timer count is altered in unconsiderable amount owing to generating of thin pulses in the count
input signals.
Therefore, select the timer count source before set the value to the prescaler and the timer.
(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.