USB-CTR04 Counter/Timer USB Device

Digilent's measurement computing USB-CTR04 is a USB-based, high-speed counter/timer device. It features four counter inputs, 48 MHz input frequency, up to 64-bit resolution, up to 8 MB/s scan rates, multiple counter modes, four pulse-width modulation (PWM) timers, and eight digital I/O. This device is USB-powered and requires no external power.

The USB-CTR04 device provides high-speed counter/timer operations synchronized with digital I/O functions. The four-channel USB-CTR04 features high frequency and scan rates, debounce filtering, support for multiple counting modes, and software-selectable resolution up to 64 bits. The device also provides eight individually configurable digital I/O channels.

USB-CTR04 supports an aggregate throughput rate of 8 MB/s. The device can be configured for any resolution up to 64 bits, eliminating the need to cascade counters. The data streaming rates for these common resolution settings are 16-bit: 4 MS/s, 32-bit: 2 MS/s, and 64-bit: 1 MS/s. Each counter channel has a connection point for counter input, counter output, and counter gate.

Counter inputs can be read asynchronously under program control or synchronously with digital inputs as part of a digital scan group. In both cases, counters can be configured to function as counter resets to 0 after each read, counter counts up or down and then rolls over at a user-set limit, or counter counts until the user-set limit has been reached. Counter inputs can concurrently monitor time periods, frequencies, pulses, and other event-driven incremental occurrences directly from pulse generators, limit switches, proximity switches, and magnetic pick-ups. Counter gates use input signals to clear a counter, change counter direction, or start/stop counting. Gate options are software selectable. Counter outputs can be used to control or transmit signals to external devices and to counter inputs, counter gates, or digital inputs.

The USB-CTR04 supports totalize mode (event counter), period measurement mode, pulse-width measurement mode, and timing measurement mode. Counter input modes are software selectable. Some modes include the max limit and the min limit register values, which do not directly affect the current count but set limits in some modes to determine counter behavior.

In period measurement mode, the device measures the period of any signal at a counter input (CxIN). The device counts the integral number of ticks that make up the period, and the data returned is always time measured in ticks. The measurement period is the time from edge-to-edge, either both rising or both falling. Period data is latched as it becomes available and is acquired at the counter read rate. The data returned is interpreted as time measured in ticks. This data represents the number of tick size intervals counted during the period measurement.

In pulse width measurement mode, the device measures 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. 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.

In timing mode, the device measures the time between an event on the counter input (CxIN) and a subsequent event on the counter gate (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).

The USB-CTR04 has debounce circuitry, which eliminates switch-induced transients that are typically associated with electromechanical devices, including relays, proximity switches, and encoders. All debounce filter options are software selectable. Users can select a debounce time, debounce mode, and rising-edge or falling-edge sensitivity. Each channel can be debounced with 16 programmable debounce times ranging from 500 ns to 25.5 ms. The signal from the buffer can be inverted before it enters the debounce circuitry. The inverter is used to make the input rising edge or falling-edge sensitive.

The USB-CTR04 has eight digital I/O lines. The digital I/O connectors can detect the state of any TTL-level input.

The USB-CTR04 includes four 32-bit timer outputs. Each timer can generate a programmable width pulse with a software-selectable frequency of 0.02235 Hz to 48 MHz. At higher frequencies, the timer output frequency and duty cycle depend on the load impedance and the supply. The timer output rate and pulse width can be updated asynchronously at any time; however, doing so results in a pulse stream that is not seamless.

Users can pace synchronous acquisition of counter data by the onboard clock or by an external clock connected to the external clock input connector.

Software support includes DAQami, an out-of-the-box application for data logging, visualization, and signal generation. Data can be viewed in real-time or post-acquisition on user-configurable displays. Drivers are included for the most popular applications and programming languages, including Visual C++®, Visual C#®, Visual Basic® .NET, DASYLab®, LabVIEW™, and Python™.