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|''PPI Port C Bit''||||''PSG Function''
|-
|7||6
Note:
The "inactive" mode must be used between function changes. If it is not used then there will be problems with the program on the CPC+. See the document about CPC+ extra information for a description of this.
The "inactive" mode can be used to prevent register corruption between changing modes.
== Programming the PSG==
The PSG has 16 internal registers and these control the operation. Before a register can be read from/written to it must be selected.
=== Register selection===
To write data to the PSG, PPI Port A must be operating as output. (See the document on the 8255 to see how to do this)
The register will remain selected until another is chosen.
=== Writing to the selected PSG register===
To write data to the PSG, PPI Port A must be operating as output. (See the document on the 8255 to see how to do this)
write data to PPI Port A,
set bit 7 to "1" and bit 6 to "0" of PPI Port C
The data will then be written into the register.
Reading from the selected PSG register
To read data from the PSG, PPI Port A must be operating as input. (See the document on the 8255 to see how to do this)
Notes
If the tone period is in the range 0-4 I can not hear any tone output.
Programming Examples
ret
=== Writing to a PSG register. ===
This routine can be used to write to registers on the PSG. C contains the index of the PSG register to write. A contains the data to write to the PSG register.