IOtech DaqBoard/3000USB Series, User Manual

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Encoder Mode
(see page 15).
OPT[1:0] : Determines the encoder measurement mode: 1X, 2X, or 4X.
OPT2 : Determines whether the counter is 16-bits (Counter Low); or 32-bits (Counter High).
OPT3 : Determines which signal latches the counter outputs into the data stream going back to the
/3000USB Series board. Start of scan or mapped channel.
OPT4 : Allows the mapped channel to gate the counter.
OPT5 : Allows the mapped channel to clear the counter for Z reference.
Counter/Totalize Mode
TIP:
When using a counter for a trigger source, it is a good idea to use a pre-trigger with a value of at least 1.
The reason is that all counters start at zero with the initial scan; and there will be no valid reference in regard to
rising or falling edge. Setting a pre-trigger to 1 or more ensures that a valid reference value is present, and that
the first trigger will be legitimate.
The counter mode allows basic use of a 32-bit counter. While in this mode, the channel’s input can only
increment the counter upward. When used as a 16-bit counter (Counter Low), one channel can be scanned
at the 12 MHz rate. When used as a 32-bit counter (Counter High), two sample times are used to return the
full 32-bit result. Therefore a 32-bit counter can only be sampled at a 6 MHz maximum rate. If only the
upper 16 bits of a 32-bit counter are desired then that upper word can be acquired at the 12 MHz rate.
The first scan of an acquisition always zeroes all counters. It is usual for all counter outputs to be latched
at the beginning of each scan; however, there is an option to change this. A second channel, referred to as
the
“mapped” channel , can be used to latch the counter output. The mapped channel can also be used to:
•
gate the counter
•
increment the counter
•
decrement the counter
The mapped channel can be any of the 4 counter input channels (post-debounce), or any of the four
asynchronous read strobes. When a counter is not in the scan it can be asynchronously read with, or
without,
clear on read . The asynchronous read-signals strobe when the lower 16-bits of the counter are
read by software. The software can read the counter’s high 16-bits at a later time, after reading the lower
16-bits. The full 32-bit result reflects the timing of the first asynchronous read strobe.
Counter/Totalize Mode
*There is one asynchronous read strobe for each of the four counter channels.
5-6 Counter Input Modes
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DaqBoard/3000USB Series User’s Manual