On Interrupt Sequence - Yamaha YMF795 Manual

YMF795

■On Interrupt Sequence

An interrupt from LSI (/IRQ-"L") occurs when the amount of data in the FIFO becomes less than the setting value.
For example, supposing that 10h (16b) is set to the IRQ point of $34h, the FIFO becomes full before starting a piece as
described in "Settings and procedure required for a piece generation."
Once a piece is started, the data in the FIFO decreases as the musical score data is processed. When the amount of
remaining data becomes 16 bytes or less, /IRQ pin becomes "L" and occurrence of an interrupt is sent to the external
microprocessor.
When an interrupt signal is detected, set IRQE to "0" and write the musical score data into the FIFO before it becomes
empty. As overwriting the data into the filled FIFO is prohibited, write the data into FIFO by the amount not causing the
overwriting (16 data in this case).
Flow chart
Set each register according to the explanation of "Settings and procedure
required for a piece generation."
As a piece is played back, the musical score data are processed in the LSI.
Set the IRQ enable bit (IRQE) to "0" and write data into the FIFO.
Cautions for the write operation is the following two points:
Be sure to write data before FIFO becomes empty.
Overwriting the data into the filled FIFO is prohibited.
Start the playback.
The remaining data in FIFO is lower than
IRQ point set in the $34h ?
Yes
Do you want to stop the piece?
Yes
Stop the piece. (ST=0)
-25-
No
No