Small snippet to make the AY scream a bit

[na_th_an]

I ported some old code I developed with the aid of a couple of snippets published in Microhobby and some documentation for the AY chip to ZX Basic. The original was plain interpreted Sinclair BASIC. It may be useful to create simple sound effects, but nothing very fancy. Porting WYZ's replayer would be a better idea, but I have no time at the moment.

Try this:

Code:

Dim sonidos (4, 13) As Byte => {_
    {100,50,0,0,0,0,4,216,31,0,0,10,10,0}, _
    {250,250,0,0,0,0,15,248,31,0,0,10,10,0}, _
    {10,10,0,0,0,0,29,216,31,0,0,4,4,0}, _
    {10,100,0,0,0,0,15,248,31,0,0,50,50,0}, _
    {15,1,0,0,0,0,15,248,31,0,0,50,50,0} _
}
Dim n As Byte

Cls
For n = 0 To 4                          ' We'll play 4 sounds
    Print "SFX #"; n                    ' Print which one
    ayPlaySound (n)                     ' Play sound # i
    Pause 100                           ' Wait for 2 secs.
Next n

Sub ayPlaySound (sonido As Byte)
    ' This SUB plays the sound passed as parameter
    ' Sounds are taken from table "sonidos", which
    ' must be defined globally.

    Dim i As Byte
  
    For i = 0 To 13
        Out 65533, i                    ' Select which AY register
        Out 49149, sonidos (sonido, i)  ' Write a value in it
    Next i
End Sub

The values in the array are pretty straightforward. The first 14 AY registers are written by the routine, just look at this table and you may create your own wacky sounds.

Code:

AY REGISTERS

00              Channel A fine pitch            8-bit (0-255)
01              Channel A course pitch          4-bit (0-15)
02              Channel B fine pitch            8-bit (0-255)
03              Channel B course pitch          4-bit (0-15)
04              Channel C fine pitch            8-bit (0-255)
05              Channel C course pitch          4-bit (0-15)
06              Noise pitch                     5-bit (0-31)
07              Mixer                           8-bit (see below)
08              Channel A volume                4-bit (0-15, see below)
09              Channel B volume                4-bit (0-15, see below)
10              Channel C volume                4-bit (0-15, see below)
11              Envelope fine duration          8-bit (0-255)
12              Envelope course duration        8-bit (0-255)
13              Envelope shape                  4-bit (0-15)
14              I/O port A                      8-bit (0-255)
15              I/O port B                      8-bit (0-255)

Bit:
7       6        5        4        3        2        1        0
_         _
I/O     I/O     Noise    Noise    Noise     Tone     Tone     Tone
B        A        C        B        A        C        B        A