Changes
/* Memory Mapped I/O Ports */
POR column indicates whether a register has power on reset. A "N" indicates that the contents of a register are undefined at power on.
Sprite magnification is coded in 1 byte:
* bits3..2 are X magnification (00 = not displayed, 01 = x1, 10 = x2, 11 = x4)
* bits1..0 are Y magnification (00 = not displayed, 01 = x1, 10 = x2, 11 = x4)
A colour in the palette is coded in 2 bytes:
* For first byte, bits7..4 are blue value, bits3..0 are red value
* For second byte, bits7..4 are ignored, bits3..0 are green value
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