For developers wanting to explore FCM (full-colour mode), it can be quite a daunting journey initially, so here’s some pointers along with an ‘experimentation’ walkthrough that will let you peek and poke your way to a better understanding of FCM 
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I need to divide this by 64 bytes ($40) to get the char index
(since each pixel within the 8x8 character needs one byte in FCM mode)I.e., $4,0000 / $40 = $1000
So you need to set:
Screen RAM byte 0 to $00
Screen RAM byte 1 to $10
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What’s all this about 16-bit character numbers?!
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The docs for CHR16 say it enables "16-bit character numbers", when in reality, it enables “13-bit character numbers” (i.e., bits 0-12 defined in the two fields above)
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