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<p class=rvps2><span class=rvts10>NES Scrolling 2</span></p>
<p>nes scrolling</p>
<p><br></p>
<p>Date: Tue, 13 Apr 1999 17:48:54 -0600</p>
<p>From: loopy <zxcvzxcv@netzero.net></p>
<p>Reply-To: nesdev@onelist.com</p>
<p>To: nesdev@onelist.com</p>
<p><br></p>
<p>From: loopy <zxcvzxcv@netzero.net></p>
<p><br></p>
<p>(more notes on ppu logic)</p>
<p><br></p>
<p>you can think of bits 0,1,2,3,4 of the vram address as the "x scroll"(*8)</p>
<p>that the ppu increments as it draws. as it wraps from 31 to 0, bit 10 is</p>
<p>switched. you should see how this causes horizontal wrapping between name</p>
<p>tables (0,1) and (2,3).</p>
<p><br></p>
<p>you can think of bits 5,6,7,8,9 as the "y scroll"(*8). this functions</p>
<p>slightly different from the X. it wraps to 0 and bit 11 is switched when</p>
<p>it's incremented from _29_ instead of 31. there are some odd side effects</p>
<p>from this.. if you manually set the value above 29 (from either 2005 or</p>
<p>2006), the wrapping from 29 obviously won't happen, and attrib data will be</p>
<p>used as name table data. the "y scroll" still wraps to 0 from 31, but</p>
<p>without switching bit 11. this explains why writing 240+ to 'Y' in 2005</p>
<p>appeared as a negative scroll value.</p>
<p><br></p>
<p class=rvps3><span class=rvts11>2008</span></p>
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