Changes
Registers R16 and R17 function as intermediate data storage registers between the PSG/CPU data bus (DA0--DA7) and the two I/O ports (IOA7--IOA0 and IOB7--IOB0). Both ports are available in the AY-3-8910; only I/O port A is available in the AY-3-8912; none are available on the AY-3-8913. Using registers R16 and R17 for the transfer of I/O data has no effect on sound generation.
== D/A Converter Operation ==
Since the primary use of the PSG is to produce sound for the highly imperfect amplitude detection mechanism of the human ear, the D/A conversion is performed in logarithmic steps with a normalized voltage range of from 0 to 1 Volt. The specific amplitude control of each of the three D/A Converters is acomplished by the three sets of 4-bit outputs of the Amplitude Control block, while the Mixer outputs provide the base signal frequency (Noise and/or Tone).
|0||0||x||x||[[Image:psg1.gif]]
|-
|0||1||x||x ||[[Image:psg3.gif]]
|-
|1||0||0||0 ||[[Image:psg5.gif]]
|-
|1||0||0||1 ||[[Image:psg1.gif]]
|-
|1||0||1||0 ||[[Image:psg8.gif]]
|-
|1||0||1||1 ||[[Image:psg4.gif]]
|-
|1||1||0||0 ||[[Image:psg6.gif]]
|-
|1||1||0||1 ||[[Image:psg2.gif]]
|-
|1||1||1||0 ||[[Image:psg7.gif]]
|-
|1||1||1||1 ||[[Image:psg3.gif]]
|}
'''Fig 2. DETAIL OF TWO CYCLES Of Fig 1 (ref. waveform "1010" in Fig.1)'''
'''Fig 3. D/A CONVERTER OUTPUT'''
'''Fig 4. SINGLE TONE WITH ENVELOPE SHAPE/CYCLE PATTERN 1010'''
'''Fig 5. MIXTURE OF THREE TONES WITH FIXED AMPLITUDE'''
== ELECTRICAL CHARACTERISTICS (AY-3-8910, AY-3-8912) ==
