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<title>9.2 The ST20 timers on the ST20C2</title>
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<a name="1204472"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">9.2 The ST20 timers on the ST20C2</font>
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<a name="1204473"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The ST20C2 processor has two on-chip real-time 32-bit clocks, called timers, one with low resolution and one with high resolution. The following details are relevant for some ST20C2 devices. You should check the figures given in the device datasheet as the timing values vary with different processor revisions.</font>
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<a name="1204474"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The low resolution clock can be used for timing periods up to approximately 38 hours, with a resolution of 64 <font face="Symbol">m</font>sec. The low resolution clock is accessed by low priority tasks. The high resolution clock can be used for timing periods up to approximately half an hour with a resolution of 1 <font face="Symbol">m</font>sec. The high resolution clock is accessed by high priority tasks. Longer periods can be timed with either timer by explicitly incrementing a counter.</font>
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<a name="1204475"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The clocks start at an undefined value and wrap round to 0 on the next tick after 0xFFFF燜FFF, or, if treated as signed, to the most negative integer on the next tick after the most positive integer. The tick rate of the clocks is derived from the processor input <span class=Signal>ClockIn</span>, and the speed and accuracy depends on the speed and accuracy of the input clock.</font>
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<a name="1204476"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">For ST20 variants with power-down capability, the clocks pause when the ST20 is in power-down mode.
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<caption><b><i><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205756"> </a><font face="Helvetica">Table 16: Summary of clock intervals for parts operating at 40燤hz</font></font></i></b></caption>
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<th><font face="Verdana, Arial, Helvetica, sans-serif" color="#003366"><a name="1205732"> </a><font face="Verdana, Arial, Helvetica, sans-serif">Parameter</font></font></th>
<th><font face="Verdana, Arial, Helvetica, sans-serif" color="#003366"><a name="1205734"> </a><font face="Verdana, Arial, Helvetica, sans-serif">Low priority</font></font></th>
<th><font face="Verdana, Arial, Helvetica, sans-serif" color="#003366"><a name="1205736"> </a><font face="Verdana, Arial, Helvetica, sans-serif">High priority</font></font></th>
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<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205738"> </a><div ><font size=2>Interval between ticks</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205740"> </a><div ><font size=2>64 <font face="Symbol">m</font>s</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205742"> </a><div ><font size=2>1 <font face="Symbol">m</font>s</font></div></font></td>
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<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205744"> </a><div ><font size=2>Ticks per second</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205746"> </a><div ><font size=2>15625</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205748"> </a><div ><font size=2>1000000</font></div></font></td>
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<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205750"> </a><div ><font size=2>Approximate full timer cycle</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205752"> </a><div ><font size=2>76.35 hours</font></div></font></td>
<td><font face="Verdana, Arial, Helvetica, sans-serif"><a name="1205754"> </a><div ><font size=2>1.193 hours</font></div></font></td>
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