Audio, Disk, UART Control Write
| Bit | Function | Description |
|---|---|---|
| 15 | SET/CLEAR | Set/clear control bit.determines if bits written with a 1 get set or cleared.bits written with a zero are always unchanged. |
| 14-13 | PRECOMP 1-0 | 00 : none 01 : 140 ns 10 : 280 ns 11 : 560 ns |
| 12 | MFMPREC | (1 = MFM precomp / 0 = GCR precomp) |
| 11 | UARTBRK | Forces a UART break (clears TXD) if true |
| 10 | WORDSYNC | Enables disk read synchronizing on a word equal to DISK SYNC CODE, Located in address DSKSYNC (7E). |
| 09 | MSBSYNC | Enables disk read synchronizing on the MSB (most significant bit) appl type GCR |
| 08 | FAST | Disk data clock rate control : 1 : fast(2us) 0 : slow(4us) (Fast for MFM or 2us,slow for 4us GCR) |
| 07 | USE3PN | Use audio channel 3 to modulate nothing |
| 06 | USE2P3 | Use audio channel 2 to modulate period of channel 3 |
| 05 | USE1P2 | Use audio channel 1 to modulate period of channel 2 |
| 04 | USE0P1 | Use audio channel 0 to modulate period of channel 1 |
| 03 | USE3VN | Use audio channel 3 to modulate nothing |
| 02 | USE2V3 | Use audio channel 2 to modulate volume of channel 3 |
| 01 | USE1V2 | Use audio channel 1 to modulate volume of channel 2 |
| 00 | USE0V1 | Use audio channel 0 to modulate volume of channel 1 |
Note: If both period and volume are modulated on the same channel, the period and volume will be alternated. First AUDxDAT word is used for V6-V0 of UDxVOL. Second AUDxDAT word is used for P15-P0 of AUDxPER. This alternating sequence is repeated.