Measurement Computing USB-CTR04 - Manual (Page 9)

USB-CTR04 User's Guide Functional Details
Counter input modes
The USB-CTR04 supports the following counter input modes:

Totalize
 Period measurement
 Pulse-width measurement
 Timing measurement
Counter input modes are programmable with software. Some modes include software-selectable max limit and
min limit register values . These values do not directly affect the current count, but set limits in some modes to
determine counter behavior.
Each mode supports additional counter operation options. Refer to the discussion of each counter mode in the
pages that follow for specific information.
Totalize mode
You can use the USB-CTR04 as a high speed pulse counter for general counting applications.
Each counter can be set to any resolution up to 64-bits based on the software-selectable max limit and min limit
register values. The counters can accept frequency inputs up to 48 MHz.
In totalize mode,
CxIN
is used as the primary counter input.
CxGT
can be used to set the count direction, to gate
the counter, to clear/reload the counter with the min limit value, or to trigger a particular counter to begin
counting.
All totalize measurement mode options are software-selectable. Each option is explained in the table below.
Totalize counter mode options
Counter option Description
Clear on read The counter is cleared after each read (synchronous or asynchronous). The value of the counter
before it was cleared is latched and returned. It is typically cleared to zero, but depending on
counting mode, it may be cleared to the value stored in the min limit register.
Range Limit When the range limit option is enabled, you can set the max limit and the min limit register values to
mimic limit switches in a mechanical counter.

When counting up, the counter freezes or rolls over to the min limit count whenever the count
reaches the max limit register value.

When counting down, the counter freezes or rolls over to the max limit count whenever the count
reaches the min limit register value
Non-recycle The counter freezes if the max limit or the min limit is reached.

When counting up, the counter stops when the max limit is reached.

When counting down, the counter stops when the min limit is reached.
Counting resumes if the direction is reversed or if the counter is reloaded with a value between the
max limit and the min limit.
CountDown Enables count down mode. (This is overridden by the state of the gate input if the gate is
programmed for direction control.)
Output On Enables counter output mode. Based on the output initial state of the counter (high or low), the
counter output toggles the state of the counter when it reaches the value of output register 0, and
toggles back to output initial state of the counter when the it reaches the value of output register 1.
Output Initial
State
Sets the initial state of the counter output to either high or low (default).
9