ABB 57160001-UH DSTD150A编码器
通过在回读命令中将计数位（D5）和状态位（D4）设置为零（0），可以同时锁存指定计时器的计数和状态。如果使用此技术，计时器的第一次读取操作将返回状态，而接下来的一次或两次读取（取决于计时器是否编程为一个或两个字节）将返回计数。成功读取将返回未锁定计数。模式定义VMIVME-7740使用82C54定时器/计数器作为定时器。82C54定时器/计数器可编程为在六种不同模式下工作（编号为模式0至模式5）。VMIVME-7740定时器是配置为使用模式2运行的硬件。仅定义了模式2。模式2用作除以N计数器。一旦控制字和初始计数被写入计时器，初始计数将被加载到下一个时钟周期。当计数减至1时，产生中断。然后计时器重新加载初始计数，并重复该过程。此模式是周期性的。对于初始计数N，序列每N个CLK循环重复一次。初始计数为1是非法的。
Both the count and status of the specified Timer(s) can be latched at the same time by setting both the Count bit (D5) and Status bit (D4) to zero (0) in the Read-Back command. If this technique is used, the first read operation of the Timer will return the status while the next one or two reads (depending on whether the Timer is programmed for one or two bytes) will return the count. Succeeding reads will return unlatched counts.Mode Definitions The VMIVME-7740 utilizes an 82C54 Timer/Counter for its Timers. 82C54 Timer/Counters can be programmed to function in six different modes (numbered Mode 0 through Mode 5). The VMIVME-7740 Timers are hardware configured to operate using Mode 2. Only Mode 2 is defined. Mode 2 functions as a divide by N counter. Once a Control Word and an initial count are written to the Timer, the initial count is loaded on the next Clock cycle. When the count decrements to 1 an interrupt is generated. The Timer then reloads the initial count and the process repeats. This Mode is periodic. For an initial count of N, the sequence repeats every N CLK cycles. An initial count of 1 is illegal.
