Turbo Sound Next Control
From SpecNext official Wiki
| Number | $FFFD |
|---|---|
| Decimal | 65533 |
| Short desc. | Controls stereo channels and selects active sound chip and sound chip channel. |
| Bit Mask | %11-- ---- ---- --0- |
| Readable | Yes |
| Writable | Yes |
| Subsystem | Turbo Sound Next |
There are three AY chips in the zx next whose selection is made through port 0xFFFD. The currently active AY chip continues to use port 0xFFFD for register select and port 0xBFFD for data. All AY chips generate stereo sound unless placed in mono mode per nextreg 0x08 and nextreg 0x09. The Next adds port 0xBFF5 to read information about the currently selected AY chip and its currently selected register.
When read, returns the value stored in the selected register on the active AY chip
When written to with the top bit set, selects the active sound chip.
| Bit | Function |
|---|---|
| 7 | Must be 1 |
| 6 | Enable left audio |
| 5 | Enable right audio |
| 4-2 | Must be 1 |
| 1-0 | Select active chip. 0-3: unused, AY3, AY2, AY1. |
Otherwise, selects the register number to access from the active sound chip.