The Motion Capture card comes with a choice of full featured, software drivers that provide a programmatic interface to the functions of the card. The following features apply to all driver types:

• Detailed Control of All Interface Parameters - The driver software provides programmatic control over all of the interface parameters and operating modes. These include signal types, termination, and signal decode modes (quadrature 1X, 4X and step and direction).
• Two Ways to Measure Position - The drivers support two types of position measurements on each encoder channel:
  • A strobed position measurement that corresponds to the value of the encoder position counter at the sampling time.
  • An edge time and position measurement (armed position) that reflects the time and position at the instant the encoder generated a pulse. These time/position value pairs provide a more accurate relationship between time and position and allow you to very accurately compute velocity and acceleration.
• Automatic Handling of Counter Over/Under Flow - The driver software (with the help of hardware circuitry) automatically extends and converts the 32 bit encoder counters to a 64 bit floating point representation. The automatic handling of counter over/under flow and sign reversal means the driver always returns accurate position/time information during reading.
• Measurements Specified at a High-Level - The measurements to make are simply specified as a list of items to measure. Each item is specified using a triplet consisting of: (1) the board number, (2) the encoder channel, and (3) the measurement type. The driver software handles all of the details of configuring and connecting encoder channels. The resulting measurements are simply read from the driver as an array of time/position values.
• Sampling Specifications at the Timebase Level - Specifying how individual encoder channels are sampled is done at the concept of a timebase. A timebase is used to control the rate and the period of time over which encoder inputs are sampled. The timebase can be configured to sample: every M seconds or pulses of an encoder input and continue sampling for N seconds, pulses of an encoder input, or samples (or forever) The driver takes care of complex counter and multiplexer programming and reduces the task of specifying an acquisition to: Sample every M pulses of something for N pulses of something else.
• Transparent Interrupt Support - The motion capture card provides programmable hardware to support interrupt-based reading of measurements. The use of interrupts allows acquisitions to occur in the background and allows an application to capture a large number of samples at high speed without over-filling the on-board memory. The task of using interrupts is taken care of by a simple driver call that either enables or disables interrupt support.
• Low Level Support As Well - The driver also supports a set of lower level functions that allow the user to control detailed operations for those cases where it is required.

C DLL Driver Example

The example shown on the reverse side uses one Motion Capture card set to address 330 Hex to capture the strobed position of encoders attached to channels 0 and 1. Both channels 0 and 1 are programmed to accept RS422 signals with 120 Ohm termination. The inputs are programmed to interpret the input signals as Quadrature 1X signals. 20 two channel samples are acquired at a rate of 1mS per sample. The read function is told to read and return immediately if data is not available (no timeout).

 Main() {    // Read variables    unsigned long        samplesRead;    TMotionCaptureSample sampleBuffer[40];  // 20 samples PER channel    short                error, status, dataRateStatus;    // Initialize and configure variables    unsigned short        brdList[2]        = { 0, 0 };    unsigned short        chanList[2]       = { 0, 1 };    unsigned short        msrTypeList[2]    = { 0, 0 };    unsigned short        brdInitList[1]    = {0};    unsigned short        addrInitList[1]   = {0x330};                         if( (error = ER_MC_Initialize(brdInitList, addrInitList, 1, ".\\")) ) {       printf("Error: %d during initialization()\n",error);       return( 0 );            }      ER_MC_ConfigureEncoderInputMode( 0, 0, 0 );           // Encoder 0, 1X mode    ER_MC_ConfigureEncoderInputMode( 0, 1, 0 );           // Encoder 1, 1X mode    ER_MC_ConfigureEncoderInputInterface( 0, 0, 0, 1 );   // Enc 0, RS422, 120 Ohm    ER_MC_ConfigureEncoderInputInterface( 0, 1, 0, 1 );   // Enc 1, RS422, 120 Ohm     ER_MC_SetMeasurementList( brdList, chanList, msrTypeList, 2 );      // what to measure    ER_MC_ConfigureTimebaseSamplingByTimeForSampleCount(0.001, 20 );    // How to sample       ER_MC_TimebaseStart();        // Start sampling             ER_MC_Read( sampleBuffer, 40, &samplesRead, &status, 0.0, (short *)0, 1, &dataRateStatus);    // We have just read samplesRead new samples.  Now we can either process the    // samples read in sampleBuffer or accumulate the samples for later processing    // and call ER_MC_Read() again to read more samples     ER_MC_Close(); } 

LabView Example

The LabView driver for the Motion Capture cards adheres to LabView conventions. Below is a simple example that illustrates the measurement of position on encoder 1 using the two position measurement techniques (strobed and armed position) available with the Motion Capture card. Notice how the time and position value pairs of the armed position measurement more accurately predict the behavior of the encoder.

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