Measurement Computing DaqBoard 3000USB Series - Manual (Page 67)

DaqBoard/3000USB Series User’s Manual 887794 Counter Input Modes 5-5
Terms Applicable to Counter Modes
The following terms and definitions are provided as an aid to understanding counter modes.
Gating: Any counter can be gated by the mapped channel. When the mapped channel is high, the
counter will be allowed to count, when the mapped channel is low, the counter will not count but hold its
value.
Mapped Channel: A mapped channel is one of 4 signals that can get multiplexed into a channel’s
counter module. The mapped channel can participate with the channel’s input signal by gating the counter,
clearing the counter, etc. The 4 possible choices for the mapped channel are the 4 input signals (post
debounce).
Start of Scan: The start of scan is a signal that is internal to the 3000USB Series board. It signals the
start of a scan group and therefore pulses once every scan period. It can be used to clear the counters and
latch the counter value into the acquisition stream.
Terminal Count: This signal is generated by the counter value. There are only two possible values for
the terminal count: 65,535 for a 16-bit counter (Counter Low); and 4,294,967,295 for a 32-bit counter
(Counter High). The terminal count can be used to stop the counter from rolling over to zero.
Ticksize: The ticksize is a fundamental unit of time and has four possible settings: 20.83ns, 208.3ns,
2083ns, 20833ns. For measurements that require a timebase reference like period or pulsewidth, the
ticksize is the basic unit of time. Ticksize is derived from the period of the 48 MHz system clock. The
count value returned in the scan is the number of ticks that make up the time measurement.
Counter Options
The following mode options are available with the /3000USB Series board and are detailed in the
upcoming pages.
A separate block diagram has been created for each mode. Note that the OPT numbers relate to
sections of the block diagrams.
Counter/Totalize Mode (see page 6):
OPT0: Selects totalize or clear on read mode.
OPT1: Determines if the counter is to rollover or “stop at the top.”
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 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 decrement the counter.
OPT6: Allows the mapped channel to increment the counter.
Period Mode (see page 8):
OPT[1:0]: Determines the number of periods to time, per measurement (1, 10, 100, 1000).
OPT2: Determines whether the period is to be measured with a 16-bit (Counter Low);
or 32-bit (Counter High).
OPT4: Allows the mapped channel to gate the counter.
OPT6: Allows the mapped channel to be measured for periods.
Pulsewidth Mode (see page 11):
OPT2: Determines whether the pulsewidth is to be measured with a 16-bit counter (Counter Low);
or a 32-bit counter (Counter High).
OPT4: Allows the mapped channel to gate the counter.
OPT6: Allows the mapped channel to be measured for pulsewidth.
Timing Mode (see page 13).
OPT2: Determines whether the time is to be measured with a 16-bit counter (Counter Low);
or a 32-bit counter (Counter High).