ADLINK DAQ/DAQE/PXI-250x waveform generation complete guide

3. Segmented generation and stopping mode

If UC_comounter is less than the actual number of waveform samples, the waveform is "segmented" and DLY2 intervals can be inserted between each segment to achieve complex function concatenation (such as sine, triangle, sawtooth sequences). Stop mode provides three options:

Mode I: Stop immediately.

Mode II: Stop after completing the current complete waveform.

Mode III: Stop after completing the current integer multiple of iterations.

Users can flexibly choose according to their needs to ensure the integrity of the output waveform.

4. Flexible application of reference sources

Each DAC can independently select an internal 10V reference or an external reference (± 10V), and the external reference can be fine tuned through the onboard calibration circuit. Using the multiplication property of DAC, output=digital code x reference voltage. If an external reference is applied with a sine wave, amplitude modulation (AM) waveform can be directly achieved. If the external reference is different DC voltages, the output range will change accordingly. All DACs within the same group are updated synchronously to ensure that there is no phase difference in the multi-channel waveform.

Advanced triggering and synchronization

Analog trigger: can come from an external EXTATRIG pin (± 10V, 8-bit resolution) or from an ADC input signal (full range). Provide five triggering conditions: below low threshold, above high threshold, within interval, high latency, low latency, support for rising/falling edge selection and programmable latency, suitable for reliable triggering in noisy environments.

Digital triggering: Supports external TTL edge triggering.

Software trigger: triggered by internal instructions.

The System Synchronization Interface (SSI) is another powerful tool in the 250x series. It provides 7 timing signals (TIMEBASE, ADCONV, DAWR, SCAN_START, AD_TRIG, DA_TRIG, etc.) that can be shared among multiple cards. Each signal can be independently set to master/slave mode: the master card outputs the signal, while the slave card receives and replaces the internal timing. In the PXI version, these signals are transmitted through the PXI trigger bus (J2); In the PCI/PCIe version, it is achieved through a dedicated 20 pin SSI connector (ribbon cable daisy chain). With SSI, users can synchronize the analog output and acquisition of dozens or even hundreds of channels, meeting the requirements of large-scale testing systems.

External auxiliary inputs (AFI0/AFI1) allow external signals to directly replace internal ADCONV, DAWR, SCAN.START, or TIMEBASE, providing unparalleled flexibility for custom sampling/update timing.

Data Transfer and DMA

Both high-speed waveform generation and continuous acquisition require bus master DMA. This card supports Scatter/Gather DMA, which can link multiple discontinuous memory buffers into a linked list, breaking the single block continuous memory limit. It is particularly effective in multitasking systems such as Windows/Linux. The maximum transmission in non chain mode is 8MB, while there is no limit in chain mode. Once DMA is started, the hardware automatically moves the FIFO data to the host, with almost no CPU involvement. For the 8-channel 1MS/s output of 2502, with a huge amount of data, DMA is the inevitable choice.

Calibration and precision maintenance

On board precision 5V reference source (temperature drift ± 2ppm/° C, long-term stability 6ppm/1000 hours), combined with TrimDAC (multi-channel DAC) and automatic calibration circuit, can compensate for bias and gain errors. Self calibration does not require external instruments and can be completed by users through software triggering. After calibration, the constants can be stored in three user storage areas of EEPROM. It is strongly recommended to preheat for 15 minutes before calibration and remove all connecting cables. The factory default constant is stored in the factory area, and the user calibration constant can be loaded or overwritten at any time, making it easy to quickly switch between different environmental temperatures.

Universal Timer/Counter (GPTC)

Two independent 16 bit timers/counters provide 8 operating modes: Simple Gate Event Counting (Mode 1), Single Cycle Measurement (Mode 2), Single Pulse Width Measurement (Mode 3), Single Gate Pulse Generation (Mode 4), Single Trigger Pulse Generation (Mode 5), Re Trigger Single Pulse (Mode 6), Single Trigger Continuous Pulse (Mode 7), and Continuous Gate Pulse (Mode 8). All input/output polarities are programmable, and gating, clock, and counting directions can be controlled by hardware or software. These modes cover common requirements such as frequency measurement, PWM generation, and pulse delay, and can be coordinated with waveform generation (such as using GPTC output as an external trigger).

Software Support and Development

Linghua provides MAPS (Measurement, Automation, and Platform Services) suite:

MAPS Core: Driver+ACE management tool, configurable DMA buffer, alias, Board ID (via SW1 DIP switch), etc.

MAPS/LV: LabVIEW Library and Examples.

MAPS/C: C/C++API and rich examples.