DESKTOP x1k10
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                                  GI AY-3-8910   
                                 bit assignments 
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                                 General Instruments AY-3-8910
                                 Programmable Sound Generator
           Ŀ
            Selection Register  b11-b8=[b3-b0]=selected register
           
      Ŀ
       PERiod of channel A/B/C [b11-b0]=period of channel A/B/C
                                        unit=8 s
      
              Ŀ
               PERiod of NOISE  b12-b8=[b4-b0]=period of noise
                                               unit=8 s
              
                    Ŀ
                     SELECTion     b15=port B
                                       0:input
                                       1:output
                                   b14=port A
                                       0:input
                                       1:output
                                   b13=noise on channel C
                                       0:yes
                                       1:no
                                   b12=noise on channel B
                                       0:yes
                                       1:no
                                   b11=noise on channel A
                                       0:yes
                                       1:no
                                   b10=channel C
                                       0:selected
                                       1:unselected
                                    b9=channel B
                                       0:selected
                                       1:unselected
                                    b8=channel A
                                       0:selected
                                       1:unselected
                    
   Ŀ
    AMPlitude of channel A/B/C     b12=envelope
                                       0:no
                                       1:yes
                                b11-b8=[b3-b0]=amplitude of channel A/B/C
                                               logarithmic law: n+1=SQR(2)*n
   
           Ŀ
            PERiod of ENVelope [b15-b0]=period of envelope
                                        unit=128 s
           
                     Ŀ
                      ENVelope  b10-b8=[b2-b0]=envelope
                                               000:\\\\\\\\
                                               001:\_______
                                               010:\/\/\/\/
                                               011:\-------
                                               100:////////
                                               101:/-------
                                               110:/\/\/\/\
                                               111:/_______
                     
                       Ŀ
                        PORT A     b14=general purpose output            (NOT)
                                   b13=parallel port strobe              (NOT)
                                   b12=serial port data terminal ready   (NOT)
                                   b11=serial port request to send       (NOT)
                                   b10=disk B
                                       0:selected
                                       1:unselected
                                    b9=disk A
                                       0:selected
                                       1:unselected
                                    b8=disk side
                                       0:side 1
                                       1:side 0
                       
                       Ŀ
                        PORT B   b7-b0=parallel port data
                       
