add MMC5 documentation

2022-04-06 00:45:26 -05:00 · 2022-04-06 00:45:26 -05:00 · 91738dbf23
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+# Nintendo MMC5
+
+a mapper chip which made NES cartridges exceeding 1MB possible.
+
+it has two pulse channels which are very similar to the ones found in the NES, but lacking the sweep unit.
+
+additionally, it offers an 8-bit DAC which can be used to play samples. only one game is known to use it, though.
+
+# effects
+
+- `12xx`: set duty cycle or noise mode of channel.
+  - may be 0-3 for the pulse channels and 0-1 for the noise channel.