Measurement-computing USB-CTR04 Manual do Utilizador descarregar pdf (Página 11)

USB-CTR04 User's Guide Functional Details

Pulse width measurement mode

You can use the USB-CTR04 to measure the time from the rising edge to the falling edge, or vice versa, on a

counter input signal (CxIN). The measurement is either pulse width low or pulse width high, depending upon

the edge detection setting.

 If the counter read period is faster than the input period, pulse widths repeat in the acquisition. The bigger

the difference between the counter read period and the input period, the more pulse widths are repeated.

 If the counter read period is slower than the input period, then the acquisition misses some pulse widths.

The bigger the difference between the counter read period and the input period, the more pulse width

values are missed.

Decrease the counter read period in order to increase the number of different pulse widths received.

Every time the pulse width measurement is latched from the counter, the counter is immediately cleared and

enabled to count the time for the next pulse width. The pulse width measurements are latched as they become

available.

The data returned is interpreted as time measured in ticks. This data represents the number of tick size intervals

counted during the pulse width measurement.

Optionally, you can use the counter gate signal (

CxGT) to gate the counter.

 When

CxGT is high, the counter is enabled.

 When

CxGT is low, the counter is disabled, but holds the count value.

The 96 MHz system clock is used as the timing source. Pulse widths from sub-microsecond to many seconds

can be measured.

Pulse width measurement mode tick size options are software-selectable. The tick size is a fundamental unit of

time derived from the period of the 96 MHz system clock.

Four counter channel tick sizes (pulse width resolutions) are available – 20.83 ns, 208.3 ns, 2083.3 ns, and

20833.3 ns.

Timing mode

You can use the USB-CTR04 to measure the time between an event on

CxIN and a subsequent event on CxGT,

such as the rising or falling edge of one event with respect to the rising or falling edge of another event (based

on the edge detection setting).

Whenever the time measurement is latched from the counter, the counter is immediately cleared and enabled for

accepting the subsequent time period, which starts with the next edge on the main channel.

The following example measures the time between the rising edge on a counter input (

CxIN) and the falling

edge on the counter gate (

CxGT). The counter read operation returns zeroes until one complete time

measurement has been taken. Then, the value (time in ticks) is latched by the device until the next time

measurement is completed. At that time, rising edges on the counter input channel clear the counter and falling

edges on the gate input latch the output of the counter.

Figure 4. Counter input channel in timing mode

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 24 25

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