https://gbdev.gg8.se/wiki/index.php?action=history&feed=atom&title=ASM_Joypad
ASM Joypad - Revision history
2026-05-01T12:11:52Z
Revision history for this page on the wiki
MediaWiki 1.25.1
https://gbdev.gg8.se/wiki/index.php?title=ASM_Joypad&diff=888&oldid=prev
PinoBatch: It's more propagation delay than bouncing
2019-07-06T14:09:36Z
<p>It's more propagation delay than bouncing</p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 14:09, 6 July 2019</td>
</tr><tr><td colspan="2" class="diff-lineno" id="L11" >Line 11:</td>
<td colspan="2" class="diff-lineno">Line 11:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      [rP1], a</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      [rP1], a</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ; read the status of the d-pad</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ; read the status of the d-pad</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>     ; <del class="diffchange diffchange-inline">we do several </del>reads <del class="diffchange diffchange-inline">because of bouncing</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>     ; <ins class="diffchange diffchange-inline">the first first few </ins>reads <ins class="diffchange diffchange-inline">waste a few cycles to let</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>     <del class="diffchange diffchange-inline">ld      a, [rP1]</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>     <ins class="diffchange diffchange-inline">; the signals settle after bits 5 and 4 have changed</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      a, [rP1]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      a, [rP1]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      a, [rP1]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      a, [rP1]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      a, [rP1]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      a, [rP1]</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">    ld      a, [rP1]        ; keep this read</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     and    $0F            ; just keep low nibble (d-pad status)</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     and    $0F            ; just keep low nibble (d-pad status)</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      [rP1], a</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     ld      [rP1], a</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>     ; <del class="diffchange diffchange-inline">bouncing</del>...</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>     ; <ins class="diffchange diffchange-inline">signal propagation</ins>...</div></td></tr>
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PinoBatch
https://gbdev.gg8.se/wiki/index.php?title=ASM_Joypad&diff=522&oldid=prev
Xzakox: Created page with 'Reads the status of the joypad, saving it in a (byte) variable "_PAD", uses the definitions of gbhw.inc: <pre> read_pad: ; init ld a, 0 ld [_PAD], a ;…'
2012-12-08T18:40:51Z
<p>Created page with 'Reads the status of the joypad, saving it in a (byte) variable "_PAD", uses the definitions of gbhw.inc: <pre> read_pad: ; init ld a, 0 ld [_PAD], a ;…'</p>
<p><b>New page</b></p><div>Reads the status of the joypad, saving it in a (byte) variable "_PAD", uses the definitions of gbhw.inc:<br />
<br />
<pre><br />
read_pad:<br />
; init<br />
ld a, 0<br />
ld [_PAD], a<br />
<br />
; read the d-pad:<br />
ld a, %00100000 ; bit 4 = 0, bit 5 = 1 (d-pad on, buttons off)<br />
ld [rP1], a<br />
; read the status of the d-pad<br />
; we do several reads because of bouncing<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
<br />
and $0F ; just keep low nibble (d-pad status)<br />
swap a ; swap low and high nibbles<br />
ld b, a ; save d-pad status in b register<br />
<br />
; let's read the buttons<br />
ld a, %00010000 ; bit 4 = 1, bit 5 = 0 (buttons on, d-pad off)<br />
ld [rP1], a<br />
<br />
; bouncing...<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
ld a, [rP1]<br />
<br />
; we have in "a" the status of the buttons<br />
and $0F ; just keep low nibble.<br />
or b ; OR with "b" to put in the high byte of "a"<br />
; the d-pad status.<br />
<br />
; now we have in "a" the status of all the controls<br />
; make the complement of it (so activated buttons read as 1)<br />
; and save it <br />
cpl<br />
ld [_PAD], a<br />
<br />
; reset the joypad<br />
ld a,$30<br />
ld [rP1], a<br />
<br />
; return<br />
ret<br />
</pre></div>
Xzakox