3.3 Interrupt-Based AD Sample or Scan
Interrupt-based analog input operations are necessary when conversions must be performed at high sampling rates. They differ in operation from standard A/D samples and scans in that they perform a preset number of conversions per function call, rather than taking a single sample or scan. There are a number of different options that can be set for interrupt-based operations; these are explained in the interrupt-based operations chapter. The Universal Driver functions for A/D sample and scan operations are dscADSampleInt and dscADScanInt.
Create and initialize an A/D settings structure (DSCADSETTINGS).
Call dscADSetSettings and pass it a pointer to this structure in order to setup the driver for A/D operations.
Create and initialize an analog I/O interrupts structure (DSCAIOINT).
Initialize the sample_values buffer in the DSCAIOINT structure by allocating sufficient memory to store the results of the interrupt operations. The memory required is:
Memory = sizeof(WORD) * num_conversions
Call dscADSampleInt or dscADScanInt and pass it a pointer to the above-mentioned DSCAIOINT structure to begin interrupt operation. The interrupt operations will now run in a separate system thread until either they reach the maximum number of conversions specified (one-shot mode only) or they are cancelled by a call to dscCancelOp.
...
DSCB dscb;
DSCADSETTINGS dscadsettings;
DSCAIOINT dscaioint;
...
/* Step 1 */
// These are example values; your application will vary.
// See DSCADSETTINGS struct and hardware manuals for details.
dscadsettings.current_channel = 0;
dscadsettings.gain = GAIN_1;
dscadsettings.range = RANGE_5;
dscadsettings.polarity = UNIPOLAR;
dscadsettings.load_cal = 0;
/* Step 2 */
if ((result = dscADSetSettings(dscb, &dscadsettings)) != DE_NONE)
return result;
/* Step 3 */
dscaioint.num_conversions = 1024;
dscaioint.conversion_rate = 10000;
dscaioint.cycle = FALSE;
dscaioint.internal_clock = TRUE;
dscaioint.low_channel = 0;
dscaioint.high_channel = 3;
dscaioint.external_gate_enable = FALSE;
dscaioint.internal_clock_gate = FALSE;
dscaioint.fifo_enab = TRUE;
dscaioint.fifo_depth = 256;
dscaioint.dump_threshold = 512;
/* Step 4 */
dscaioint.sample_values = (WORD*) malloc(sizeof(WORD) * dscaioint.num_conversions);
memset(dscaioint.sample_values, 0, sizeof(WORD) * dscaioint.num_conversions);
/* Step 5 */
if ((result = dscADScanInt(dscb, &dscaioint)) != DE_NONE)
return result;
...
NOTE: Boards can only achieve interrupt rates that divide evenly into their onboard counters, so the driver will attempt to find the rate closest to that which you specified.
Last modified 3yr ago