Channel-Gain Queue
Use the channel-gain queue feature to configure a list of channels and gains for each scan. Each channel can have a different gain setting, and the settings are stored in a list that is written to local memory on the device.
The channel-gain queue list on USB-1808 Series devices can contain up to eight unique channels that must be listed in increasing order.
Analog Output
USB-1808 Series devices offer two 16-bit analog outputs. USB-1808X models can be updated at a rate of 500 kS/s per channel, while USB-1808 models can be updated at a rate of 125 kS/s. The output range is fixed at ±10 V.
Digital I/O
Four digital I/O lines are individually configurable for input or output. The DIO terminals can detect the state of any TTL-level input. Users can configure for pull-up (+5 V) or pull-down (0 V) with an onboard jumper.
Counter Input
USB-1808 Series devices have two 32-bit general-purpose counter inputs that can be read asynchronously under program control, or synchronously as part of a digital scan group.
Each counter can accept frequency inputs up to 50 MHz and supports the following software-selectable counter input modes:
- Totalize – High-speed pulse counter for general counting applications. The internal counter increments when the TTL levels transition from low to high or from high to low.
- Period measurement – Measure the period of a signal at a counter channel input. Users can measure x1, x10, x100 or x1000 periods for 32-bit values. Four resolutions are available — 20 ns, 200 ns, 2000 ns, or 20,000 ns
- Pulse-width measurement – Measure the time from the rising edge to the falling edge, or vice versa, on a signal on a counter input. Four resolutions are available - 20 ns, 200 ns, 2000 ns, or 20,000 ns.
Each mode supports additional counter options. When counter options are set, the counters 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.
Quadrature Encoder Input
USB-1808 Series devices can simultaneously decode signals from up to two quadrature encoders. Encoders with a 50 MHz maximum pulse frequency and X1, X2, and X4 count modes are supported. Each device provides A, B, and Z inputs for each connected encoder. A typical encoder generates the A and B signals at a 90° phase shift with respect to each other. These signals are used to determine system position (counts), velocity (counts per second), and direction of travel or rotation.
Timer Output
Two timers can generate pulse rates of up to 50 MHz each, with programmable pulse widths down to 10 ns. 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.
Timer output operations can be paced by the internal clock or by an external clock, and can be initiated by a digital trigger.