outputs: none
</pre></td></tr></table><h2 id="constants">constants</h2><table><tr><th>constants</th><th>description</th><th>value</th></tr><tr><td id="screen_current_col">screen_current_col</td><td></td><td>$d3
</td></tr><tr><td id="screen_current_row">screen_current_row</td><td></td><td>$d6
</td></tr></table><h2>implementation</h2><pre id="code">
.export print_a
.export print_cr
.export cls
.export beep
.export print_a_inverse
.import timer_read
.exportzp screen_current_row
.exportzp screen_curre