Details
D3 | D2 | D1 | D0 | Type of Noise or Div |
0 | 0 | 0 | 1 | 4 bit poly |
0 | 0 | 1 | 0 | div 15 -> 4 bit poly |
0 | 0 | 1 | 1 | 5 bit poly -> 4 bit poly |
0 | 1 | 0 | 0 | div 2 : pure tone |
0 | 1 | 0 | 1 | div 2 : pure tone |
0 | 1 | 1 | 0 | div 31 : pure tone |
0 | 1 | 1 | 1 | 5 bit poly -> div 2 |
1 | 0 | 0 | 0 | 9 bit poly (white noise) |
1 | 0 | 0 | 1 | 5 bit poly |
1 | 0 | 1 | 0 | div 31 : pure tone |
1 | 0 | 1 | 1 | set last 4 bits to 1 |
1 | 1 | 0 | 0 | div 6 : pure tone |
1 | 1 | 0 | 1 | div 6 : pure tone |
1 | 1 | 1 | 0 | div 93 : pure tone |
1 | 1 | 1 | 1 | 5 bit poly div 6 |
Hardware Notes
This circuit contains a nine bit shift counter which may be controlled by the output code from a four bit audio control register (AUDC), and is clocked by the frequency select circuit. The control register can be loaded by the microprocessor at any time, and selects different shift counter feedback taps and count lengths to produce a variety of noise and tone qualities. The values written cause different kinds of sounds to be generated. Some are pure tones like a flute, others have various "noise" content like a rocket motor or explosion. Some experimentation will be necessary to find "your sound".
Two audio circuits are incorporated on the TIA. They are identical and completely independent, although their outputs could be combined externally into one speaker.
SECAM Compatibility
SECAM machines use PAL software with one exception. when a sound is to be turned off, it must be one by setting AUDV0/AUDV1 to 0, not by setting AUDC0/AUDC1 to 0. Otherwise, you get an obnoxious background sound.
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