YMU757B Datasheet, PDF (25/43 Pages) YAMAHA CORPORATION – MA-1C

YMU757B
Interrupt sequence
An interrupt from LSI (/IRQ-"L") occurs when the data amount in FIFO is less than the set value.
For example, supposing that 10h (16b) is set for the IRQ point of $34h, FIFO is full with the data before starting the
melody as described above under "Settings and procedure to generate melody".
Once the melody is started, the musical score data is processed and the data in FIFO reduces continuously. When the
remaining data amount becomes 16 bytes or less, the /IRQ terminal becomes "L" and an interrupt signal is transmitted to
the external microprocessor.
When an interrupt signal is detected, set "0" for IRQE and enter the musical score data into FIFO before it becomes
empty. As overwriting the data into the filled FIFO is prohibited, enter the data into FIFO by the amount not causing
overwriting (16 data in this case).
Flow chart
Execute each register setting following the steps described under
"Settings and procedure to generate melody".
Start the melody.
As the sounds are produced, the musical score data are processed in the LSI.
Has the remaining data in FIFO reduced to the IR
No
point specified by the $34h setting or less?
Yes
Set the IRQ enable bit (IRQE) to "0" and enter the data into
FIFO, observing the following precautions.
Be sure to enter the data before FIFO becomes empty.
Overwriting the data into the filled FIFO is prohibited.
Do you want to stop the melody?
No
Yes
Stop the melody. (ST=0)
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