如何在TIA Portal中使用符号方式按位访问非结构数据类型？

<p>对于<a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;s7-1200&sol;" title&equals;"查看与 S7-1200 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">S7-1200<&sol;span><&sol;a> 和 <a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;s7-1500&sol;" title&equals;"查看与 S7-1500 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">S7-1500<&sol;span><&sol;a>，可以按1位，8位，16位和32位的长度访问已经声明的变量。<&sol;p>&NewLine;<p><strong><span lang&equals;"ZH-CN"><span style&equals;"color&colon; &num;000000&semi;">描述<&sol;span><&sol;span><&sol;strong><&sol;p>&NewLine;<p><span lang&equals;"ZH-CN"><span style&equals;"color&colon; &num;000000&semi;">为了按字节、字和双字数据类型访问变量，需要：<&sol;span><&sol;span><&sol;p>&NewLine;<ul>&NewLine;<li><span style&equals;"color&colon; &num;000000&semi;">对于S7-1200（固件V2&period;0及以上）需要 <a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;step-7&sol;" title&equals;"查看与 STEP 7 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">STEP 7<&sol;span><&sol;a> &lpar;<a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;tia-portal&sol;" title&equals;"查看与 TIA Portal 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">TIA Portal<&sol;span><&sol;a>&rpar;  <&sol;span>V11&plus;SP1&plus;Update 2 &lpar;或更高版本&rpar;<&sol;li>&NewLine;<li><span style&equals;"color&colon; &num;000000&semi;">对于S7-1500需要 <a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;step-7&sol;" title&equals;"查看与 STEP 7 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">STEP 7<&sol;span><&sol;a> &lpar;<a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;tia-portal&sol;" title&equals;"查看与 TIA Portal 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">TIA Portal<&sol;span><&sol;a>&rpar;  <&sol;span><span style&equals;"color&colon; &num;000000&semi;">V12 &lpar;或更高版本&rpar;<&sol;span><&sol;li>&NewLine;<&sol;ul>&NewLine;<p><span lang&equals;"ZH">将存储区<&sol;span>&lpar; <span lang&equals;"ZH">例如<&sol;span> Byte <span lang&equals;"ZH">或<&sol;span>Word &rpar; <span lang&equals;"ZH">划分为更小的存储区<&sol;span> &lpar; <span lang&equals;"ZH">例如<&sol;span> Bool &rpar;<span lang&equals;"ZH">也称为存储器分片。图<&sol;span> 01 <span lang&equals;"ZH">所示使用符号方式对操作数按位、字节、字进行访问。<&sol;span><&sol;p>&NewLine;<p><img class&equals;"aligncenter size-full wp-image-1541" src&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;wp-content&sol;uploads&sol;2021&sol;03&sol;01&period;png" alt&equals;"" width&equals;"580" height&equals;"270" &sol;><&sol;p>&NewLine;<p><span style&equals;"color&colon; &num;000000&semi;"><span lang&equals;"ZH-CN">使用片访问可以提供更高的编程效率并且无需在变量表里进行额外的声明。<&sol;span><&sol;span><&sol;p>&NewLine;<p><span style&equals;"color&colon; &num;000000&semi;"><span lang&equals;"ZH-CN">下例所示使用符号方式按位访问。<&sol;span>"x" <span lang&equals;"ZH-CN">代表在字或字节中按位访问并且其后的数字表示相关位的偏移量。<&sol;span><&sol;span><&sol;p>&NewLine;<p><img class&equals;"aligncenter size-full wp-image-1542" src&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;wp-content&sol;uploads&sol;2021&sol;03&sol;02&period;png" alt&equals;"" width&equals;"518" height&equals;"361" &sol;><&sol;p>&NewLine;<p><span lang&equals;"ZH-CN">下图为按字节访问的例子。<&sol;span><span lang&equals;"ZH-CN"> <&sol;span><span lang&equals;"ZH-CN">这里<&sol;span> "b" <span lang&equals;"ZH-CN">代表按字节访问并且其后面的数字表示相关字节的偏移量。<&sol;span><&sol;p>&NewLine;<p><img class&equals;"aligncenter size-full wp-image-1543" src&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;wp-content&sol;uploads&sol;2021&sol;03&sol;03&period;png" alt&equals;"" width&equals;"571" height&equals;"326" &sol;><&sol;p>&NewLine;<p>"w" <span lang&equals;"ZH-CN">代表按字进行访问并且其后的数字表示相关字的偏移量。<&sol;span><&sol;p>&NewLine;<p><img class&equals;"aligncenter size-full wp-image-1544" src&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;wp-content&sol;uploads&sol;2021&sol;03&sol;04&period;png" alt&equals;"" width&equals;"570" height&equals;"324" &sol;><&sol;p>&NewLine;<p><span style&equals;"color&colon; &num;000000&semi;"><span lang&equals;"ZH-CN">在某些技术应用上，只需要一个字节变量的前<&sol;span>4<span lang&equals;"ZH-CN">位或前<&sol;span>6<span lang&equals;"ZH-CN">位（分别对应于位<&sol;span>0<span lang&equals;"ZH-CN">至位<&sol;span>3<span lang&equals;"ZH-CN">或位<&sol;span>0<span lang&equals;"ZH-CN">至位<&sol;span>5<span lang&equals;"ZH-CN">）的值用于转换字节数据类型到一个实数数据类型的值<&sol;span><span lang&equals;"ZH-CN">。<&sol;span><span lang&equals;"ZH-CN">例如，一个二进制数（二进制编码字节）转换成十进制数（实数）。字节的最低位代表数值<&sol;span>2<sup>-5<&sol;sup><span lang&equals;"ZH-CN">。这不是小数点后的位数，但是可以自动计算出十进制数据。<&sol;span><&sol;span><&sol;p>&NewLine;<table border&equals;"1" width&equals;"100&percnt;">&NewLine;<tbody>&NewLine;<tr>&NewLine;<td align&equals;"left">位5<&sol;td>&NewLine;<td align&equals;"left">位4<&sol;td>&NewLine;<td align&equals;"left">位3<&sol;td>&NewLine;<td align&equals;"left">位2<&sol;td>&NewLine;<td align&equals;"left">位1<&sol;td>&NewLine;<td align&equals;"left">位0<&sol;td>&NewLine;<&sol;tr>&NewLine;<tr>&NewLine;<td align&equals;"left">1<&sol;td>&NewLine;<td align&equals;"left">1<&sol;td>&NewLine;<td align&equals;"left">0<&sol;td>&NewLine;<td align&equals;"left">0<&sol;td>&NewLine;<td align&equals;"left">1<&sol;td>&NewLine;<td align&equals;"left">0<&sol;td>&NewLine;<&sol;tr>&NewLine;<tr>&NewLine;<td align&equals;"left">2<sup>0<&sol;sup><&sol;td>&NewLine;<td align&equals;"left">2<sup>-1<&sol;sup><&sol;td>&NewLine;<td align&equals;"left">2<sup>-2<&sol;sup><&sol;td>&NewLine;<td align&equals;"left">2<sup>-3<&sol;sup><&sol;td>&NewLine;<td align&equals;"left">2<sup>-4<&sol;sup><&sol;td>&NewLine;<td align&equals;"left">2<sup>-5<&sol;sup><&sol;td>&NewLine;<&sol;tr>&NewLine;<tr>&NewLine;<td align&equals;"left">1&comma;0<&sol;td>&NewLine;<td align&equals;"left">0&comma;5<&sol;td>&NewLine;<td align&equals;"left">0&comma;25<&sol;td>&NewLine;<td align&equals;"left">0&comma;125<&sol;td>&NewLine;<td align&equals;"left">0&comma;0625<&sol;td>&NewLine;<td align&equals;"left">0&comma;03125<&sol;td>&NewLine;<&sol;tr>&NewLine;<tr>&NewLine;<td align&equals;"left">1&ast;1&comma;0&equals;1&comma;0<&sol;td>&NewLine;<td align&equals;"left">1&ast;0&comma;5&equals;0&comma;5<&sol;td>&NewLine;<td align&equals;"left">0&ast;0&comma;25&equals;0<&sol;td>&NewLine;<td align&equals;"left">0&ast;0&comma;125&equals;0<&sol;td>&NewLine;<td align&equals;"left">1&ast;0&comma;0625&equals;0&comma;0625<&sol;td>&NewLine;<td align&equals;"left">0&ast;0&comma;03125&equals;0<&sol;td>&NewLine;<&sol;tr>&NewLine;<&sol;tbody>&NewLine;<&sol;table>&NewLine;<p>总计 &equals; 1&period;5625&period;<&sol;p>&NewLine;<p><span style&equals;"color&colon; &num;000000&semi;"><span lang&equals;"ZH-CN">如下<&sol;span><a href&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;tag&sol;scl&sol;" title&equals;"查看与 SCL 相关的文章" target&equals;"&lowbar;blank"><span class&equals;"tag-key">SCL<&sol;span><&sol;a><span lang&equals;"ZH-CN">程序的前两行将不需要的位设为&OpenCurlyDoubleQuote;<&sol;span><&sol;span><span style&equals;"color&colon; &num;000000&semi;">false<span lang&equals;"ZH-CN">”。然后，根据变化得到 2<sup>-5<&sol;sup> è¿›è¡Œæ•°æ®ç±»åž‹è½¬æ¢åŽçš„<&sol;span><&sol;span><span lang&equals;"ZH-CN"><span style&equals;"color&colon; &num;000000&semi;">数值<&sol;span><&sol;span><span lang&equals;"ZH-CN"><span style&equals;"color&colon; &num;000000&semi;">。<&sol;span><&sol;span><&sol;p>&NewLine;<p><img class&equals;"aligncenter size-full wp-image-1545" src&equals;"https&colon;&sol;&sol;www&period;xuezdh&period;com&sol;wp-content&sol;uploads&sol;2021&sol;03&sol;05&period;png" alt&equals;"" width&equals;"585" height&equals;"361" &sol;><&sol;p>&NewLine;<p><span style&equals;"color&colon; &num;ff0000&semi; font-size&colon; 10pt&semi;"><strong><span lang&equals;"ZH-CN">注意<&sol;span><&sol;strong><&sol;span><&sol;p>&NewLine;<p><span style&equals;"font-size&colon; 10pt&semi; color&colon; &num;ff0000&semi;"><span lang&equals;"ZH-CN">从<&sol;span>STEP 7 &lpar;TIA Portal&rpar; V13 以后，语法规则从 "Variable&period;X0" 改为 "Variable&period;&percnt;X0"。如上所述示例中输入"inByte&period;X0"  åŽï¼ŒSTEP 7 &lpar;TIA Portal&rpar; V13 之后的版本会自动修改为"inByte&period;&percnt;X0"。<&sol;span><&sol;p>&NewLine;