ADKCON

         +-------+-------------+-------------------------------------------+
         | BITS  | USE         | 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 | | CODE | PRECOMP VALUE |                  |
         |       |             | +------+---------------+                  |
         |       |             | | 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 synchrinizing on the    |
         |       |             | MSB (most signif 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 AUDxVOL. Second AUDxDAT word is used for
         P15-P0 of AUDxPER. This alternating sequence is repeated.