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    <p>It's a bitwise <code>or</code>, as distinct to your normal logical <code>or</code>. It basically sets the bits in the target variable if the corresponding bit in either of the source variables was set.</p> <p>For example, the expression <code>43 | 17</code> can be calculated as:</p> <pre><code>43 = 0x2b = binary 0010 1011 17 = 0x11 = binary 0001 0001 ==== ==== "or" them: 0011 1011 = 0x3b = 59 </code></pre> <p>See <a href="https://stackoverflow.com/questions/1746613/bitwise-operation-and-usage/1746642#1746642">this answer</a> for a more thorough examination of the various bitwise operators.</p> <p>It's typically used when you want to manipulate specific bits within a data type, such as control of a watchdog timer in an embedded system (your particular use case).</p> <p>You can use <code>or (|)</code> to turn bits on and <code>and (&amp;)</code> to turn them off (with the inversion of the bitmask that's used to turn them on.</p> <p>So, to turn on the <code>b3</code> bit, use:</p> <pre><code>val = val | 0x08; // 0000 1000 </code></pre> <p>To turn it off, use:</p> <pre><code>val = val &amp; 0xf7; // 1111 0111 </code></pre> <p>To detect if <code>b3</code> is currently set, use:</p> <pre><code>if ((val &amp; 0x08) != 0) { // it is set. } </code></pre> <p>You'll typically see the bitmasks defined something like:</p> <pre><code>#define B0 0x01 #define B1 0x02 #define B2 0x04 #define B3 0x08 #define B4 0x10 </code></pre> <p>or:</p> <pre><code>enum BitMask { B0 = 0x01, B1 = 0x02, B2 = 0x04, B3 = 0x08, B4 = 0x10 }; </code></pre> <p>As to what this means:</p> <pre><code>WriteIoCR (0x72, cSetWatchDogUnit|cSetTriggerSignal); </code></pre> <p>More than likely, <code>0x72</code> will be an I/O port of some sort that you're writing to and <code>cSetWatchDogUnit</code> and <code>cSetTriggerSignal</code> will be bitmasks that you combine to output the command (set the trigger signal and use a unit value for the watchdog). What that command means in practice can be inferred but you're safer referring to the documentation for the watchdog circuitry itself.</p> <p>And, on the off chance that you don't know what a watchdog circuit is <em>for,</em> it's a simple circuit that, if you don't kick it often enough (with <em>another</em> command), it will reset your system, probably by activating the reset pin on whatever processor you're using.</p> <p>It's a way to detect badly behaving software automatically and return a device to a known initial state, subscribing to the theory that it's better to reboot than continue executing badly.</p>
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    1. COThanks for the input and going the extra mile for the other stuff!
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