如果在P8-47的例子里用POSCON替换PTCON(保持逻辑结构不变)，变量Xsition的值也如同上述变化。POSCON指令在2、3、4次扫描时传递能流，5、6、7次扫描时不传递能流，8、9、10次扫描时再次传递能流，依次类推。POSCON的变化由变量Xsition跳变位的变化决定。变量Xsition的值写进一次，–般保持3个扫描期，跳变位保持相同的值3个扫描期。因而，POSCON连续不断地每隔3个扫描周期传递能流。注意:如果变量Xsition的值实际上每个扫描周期就写进一次，那么POSCON的变化就和PTCON的变化
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