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APPENDIX
3850 Group (Spec. H) 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, X and Y 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.
3.3.5 Notes on serial I/O
(1)
Notes when selecting clock synchronous serial I/O (Serial I/O1)
Stop of transmission operation
Clear the serial I/O1 enable bit and the transmit enable bit to “0” (Serial I/O1 and transmit disabled).
q Reason
Since transmission is not stopped and the transmission circuit is not initialized even if only the
serial I/O1 enable bit is cleared to “0” (Serial I/O1 disabled), the internal transmission is running
(in this case, since pins TxD, RxD, SCLK1, and SRDY1 function as I/O ports, the transmission data
is not output). When data is written to the transmit buffer register in this state, data starts to be
shifted to the transmit shift register. When the serial I/O1 enable bit is set to “1” at this time, the
data during internally shifting is output to the TxD pin and an operation failure occurs.
Stop of receive operation
Clear the receive enable bit to “0” (receive disabled), or clear the serial I/O1 enable bit to “0”
(Serial I/O1 disabled).
(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.