furnace/doc/7-systems/saa1099.md

Philips SAA1099

this was used by the Game Blaster and SAM Coupé. it's pretty similar to the AY-3-8910, but has stereo sound, twice the channels and two envelopes, both of which are highly flexible. The envelopes work like this:

• an instrument with envelope settings is placed on channel 2 or channel 5
• an instrument that is used as an "envelope output" is placed on channel 3 or channel 6 (you may want to disable wave output on the output channel)

effects

• 10xy: set channel mode.
  • x toggles noise.
  • y toggles square.
  • this effect affects either the first 3 or last 3 channels, depending on where it is placed.
• 11xx: set noise frequency.
  • this effect affects either the first 3 or last 3 channels, depending on where it is placed.
• 12xx: setup envelope. this is a bitmask.
  • bit 7 toggles the envelope.
  • bit 5 toggles whether to use a fixed frequency or lock to the frequency of channel 2 or 5.
  • bit 4 sets the envelope resolution.
  • bits 1 to 3 set the envelope shape:
    • 000: always off
    • 001: always on
    • 010: down
    • 011: down loop (saw)
    • 100: up down
    • 101: up down loop (triangle)
    • 110: up then off
    • 111: up loop (reverse saw)
  • bit 0 sets whether the right output will mirror the left one.
  • this effect affects either the first 3 or last 3 channels, depending on where it is placed.