3.3 Register 7, is a multi-function Enable register which controls the
Mixer
Control-
three Noise/Tone Mixers and the two general purpose I/O Ports.
I/O Enable
The Mixers, as previously described, combine the noise and tone
frequencies for each of the three channels. The determination of
combining neither/either/both noise and tone frequencies on each
(Register R7)
channel is made by the state of bits B5--B0 of R7.
The direction (input or output ) of the two general purpose I/O Ports
(IOA and IOB) is determined by the state of bits B7 and B6 of R7.
These functions are illustrated in the following:
Mixer Control-I/O Enable
Register R7
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