Peripheral 4 Register

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Number $09
Readable Yes
Writable Yes
Short Description Sets scanlines, AY mono output, Sprite-id lockstep, reset DivMMC mapram and disable HDMI audio.
Bit Function
7 Enables AY2 "mono" output (A+B+C is sent to both R and L channels, makes it a bit louder than stereo mode).
6 Enables AY1 "mono" output (1 = mono, 0 default)
5 Enables AY0 "mono" output (0 after Hard-reset)
4 Sprite id lockstep (1 = Sprite port-mirror Index Register ($34) and Sprite Status/Slot Select ($303B / 12347) are in lockstep, 0 default)
3 1 to reset mapram bit in DivMMC

(was "Disables Kempston mouse port ($DF)" in core 2.0)

2 1 to silence HDMI audio (hard reset = 0) (since core 3.0.5)

(was "Disables divMMC ports ($E3, $E7, $EB) if set" in core 2.0)

1-0 scanlines weight (0 after Hard-reset):

(since core3.1.1) %00 = scanlines off, %01 = scanlines 50%, %10 = scanlines 25%, %11 = scanlines 12.5%
(before: %00 = scanlines off, %01 = scanlines 75%, %10 = scanlines 50%, %11 = scanlines 25%)