IOtech DaqBoard/3000 Series, Руководство пользователя

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An explanation of the various counter options, depicted in the previous figure, follows.
COUNTER: OPT0: This selects totalize or clear on read mode.
Totalize Mode – The counter counts up and rolls over on the 16-bit (Low Counter) boundary, or on the
32-bit (High Counter) boundary. See OPT2 in regard to choosing 16-bit or 32-bit counters.
Clear On Read Mode – The counter is cleared at the beginning of every scan or synchronous read; and
the final value of the counter [the value just before it was cleared] is latched and returned to the /3000
Series board.
COUNTER: OPT1: This determines if the counter is to rollover or “ stop at the top .”
Rollover Mode - The counter continues to count upward, rolling over on the 16-bit (Counter Low)
boundary, or on the 32-bit (Counter High) boundary. See OPT2 in regard to choosing 16-bit or 32-bit
counters.
Stop at the Top Mode - The counter will stop at the top of its count. The top of the count is FFFF for the
16-bit option (Counter Low), and FFFFFFFF for the 32-bit option (Counter High).
COUNTER: OPT2: Determines whether the counter is 16-bits or 32-bits (Counter Low, or Counter
High, respectively). This only matters when the counter is using the “stop at the top” option, otherwise this
option is inconsequential.
COUNTER: OPT3: Determines which signal latches the counter outputs into the data stream back to
the /3000 Series board. Normally, the start of scan signal latches the counter outputs at the beginning of
every scan; but an option is to have the mapped signal latch the counter outputs. This mapped-signal
option allows a second signal to control the latching of the count data. This allows the user to know the
exact counter value when an edge is present on another channel. This also allows the counters to be
asynchronously read.
COUNTER: OPT4: Allows the mapped channel to gate the counter if desired. When the mapped
channel is high , the counter is enabled. When the mapped channel is low , the counter is disabled (but
holds the count value). The mapped channel can be any other input channel.
COUNTER: OPT5: Allows the mapped channel to decrement the counter . With this option the input
channel [for the counter] will increment the counter. The mapped channel can be used to decrement the
counter.
COUNTER: OPT6: Allows the mapped channel to increment the counter instead of the main
channel. This option allows the counter to be used with any other input channel (post-debounce). If the
channel’s input is used elsewhere, for example, gating another counter, the counter for this channel does
not need to go unused.
Asynchronously Reading These Counters
If the counter is in asynchronous mode the clear on read mode is available. The counter’s lower 16-bit
value should be read first. This will latch the full 32-bit result and clear the counter. The upper 16-bit
value can be read after the lower 16-bit value. Also, counters can only be asynchronously read in modes
that allow the mapped channel to latch the data, i.e., Counter and Encoder modes. However, it is possible
for the user to use that read strobe as a mapped channel elsewhere, if desired. For example, the read strobe
could be used to increment or decrement the counter.
DaqBoard/3000 Series User’s Manual
918494
Counter Input Modes 5-7