What Brad mean?

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What Brad mean?
by JJ.Loki on 2006-01-28 (#8729)
Quote(2C02 ref):

Where the PPU fetches pattern table data for an individual object is
conditioned on the contents of the sprite temporary memory element, and
$2000.5. If $2000.5 = 0, the tile index data is used as usual, and $2000.3
selects the pattern table to use. If $2000.5 = 1, the MSB of the range
result value become the LSB of the indexed tile, and the LSB of the tile
index value determines pattern table selection. The lower 3 bits of the
range result value are always used as the fine vertical offset into the
selected pattern.

my question is:
1.what is range result value? he didn't mention it before.
2. MSB mean most significant bit for most significant byte?

i have read this paragraph for many times. but i still can't figure out what does it mean......

Thank you

by Disch on 2006-01-28 (#8741)
1) He's referring to the number you get when you subtract the sprite's Y value from the current scanline number. For example if you're on scanline 15, and the sprite's Y value is 10 .. you'd have a range result value of 5. 0-7 would be "in-range" for 8x8 sprites, whereas 0-15 would be "in-range" for 8x16 sprites. If the sprite is out of range, it isn't rendered on the next scanline.

2) In this context he means the most significant bit. Or really -- he's talking about bit 3 specifically (which isn't really the most significant -- would bit 8 be? since it's a 9-bit value I thought. Oh well... he means bit 3).


This is all just a technical explaination of typical sprite rendering stuff you might already know.

by Zepper on 2006-01-28 (#8754)
Indeed, how could a 8-bit comparator be used with a 9-bit signed value??? o.O

by Anes on 2006-01-28 (#8757)
Quote:
how could a 8-bit comparator be used with a 9-bit signed value???

i dont know too much of electronics but i think an stand alone 8 bit comparator cannot compare a 9 bit value. Bit .8 is what is the result of the carry. This is becouse most electronic counters/comparators have a special pin called "carry".

by JJ.Loki on 2006-01-28 (#8761)
Thank you Fx3,Anes,and Disch. Thank you for your warmly help ^-^