Data Blocks

Both raw data and binary data can be transferred between the driver and the instrument. Data block transfer is a simple yet powerful formatting technique for transferring waveform data between drivers and instruments.

IEEE 488.2 Binary Data—"%b"

When writing binary data to or reading it from the instrument, you can use %b, %B format codes with length modifiers (h, l, z, and Z). ASCII data is represented by signed integer values. The range of values depends on the byte width specified. One-byte-wide data ranges from –128 to +127. Two-byte-wide data ranges from –32768 to +32767. An example of an ASCII waveform data string follows:

CURVE -109, -110, -109, -107, -109, -107, -105, -103, -100, -97, -90, -84, -80

Examples

This example queries a waveform. The data is in IEEE 488.2 <ARBITRARY BLOCK PROGRAM DATA> format. The number (#) sign specifies the data size. In the absence of length modifiers, the data is assumed to be of byte-size elements.

/* Waveform Query */
ViInt32 totalPoints = MAX_DATA_PTS;
ViInt8 rdBuffer[MAX_DATA_PTS];
viQueryf (io, ":CURV?\n", "%#b", &totalPoints, rdBuffer);

This example shows how to scan the preamble of waveform data returned from a scope, how to determine the number of data points in the waveform, and how to scan the array of raw binary data returned.

/* Waveform Preamble */
ViByte data[MAX_WAVEFORM_SIZE];
ViInt32 i, tmpCount, acqType;
ViReal64 xInc, xOrg, xRef, yInc, yOrg, yRef;

viQueryf (io, "WAV:PRE?\n",

"%*[^,], %ld, %ld, %*[^,], %Lf, %Lf, %Lf, %Lf, %Lf, %Lf",
&acqType, &tmpCount, &xInc, &xOrg, &xRef, &yInc, &yOrg, &yRef);

tmpCount = (acqType == 3) ? 2*tmpCount : tmpCount;
viQueryf (io, "WAV:DAT?\n", "%#b", &tmpCount, data));

Raw Binary Data—"%y"

When transferring raw binary data to or from an instrument, use the %y format code with length modifiers (h and l) and byte ordering modifiers (!ob and !ol). Raw binary data can be represented by signed integer values or positive integer values. The range of the values depends on the specified byte width:

Examples

This example shows how to send a block of unsigned short integer (16 bits) in binary form to the instrument. In this case, the binary data is an arbitrary waveform. The asterisk (*) specifies the block size to be passed in from the argument. Also, !ob specifies data is sent in standard (big endian) format. Use !ol to send data in little endian format.

/* Create Arbitrary Waveform */
ViInt32 wfmSize = WFM_SIZE;
ViUInt16 dataBuffer[WFM_SIZE]; /* contains waveform data */
dataBuffer[WFM_SIZE-1] |= 0x1000;
/* Add the end of waveform indicator */
viPrintf (io, "STARTBIN 0 %d;%*!obhy", wfmSize, wfmSize, dataBuffer);

This example shows how to send a block of signed integers (32 bits) in binary form to the instrument. The asterisk (*) specifies the block size to be passed in from the argument. Without the presence of a byte order modifier, data is sent in standard (big endian) format.

/* Create FM Modulation Waveform */
ViInt32 dataBuffer[WFM_SIZE];
/*contains waveform data */
viPrintf (io, "%*ly", wfmSize, dataBuffer);