Technical data

316 Agilent Signal Generators Programming Guide
Creating and Downloading User–Data Files
User File Data (Bit/Binary) Downloads (E4438C and E8267D)
You download a user file to either the Bit or Binary memory catalog (directory). Unlike a PRAM file
(covered later in this chapter), user file data does not contain control bits, it is just data. The signal
generator adds control bits to the user file data when it generates the signal. There are two ways
that the signal generator uses the data, either in a continuous data pattern (unframed) or within
framed boundaries. Real–time Custom uses only unframed data, real–time TDMA modulation formats
use both types, and the others use only framed data.
NOTE For unframed data transmission, the signal generator requires a minimum of 60 symbols. For
more information, see “Determining Memory Usage for Custom and TDMA User File Data” on
page 321.
You create the user file to either fill a single timeslot/frame or multiple timeslots/frames. To create
multiple timeslots/frames, simply size the file with enough data to fill the number of desired
timeslots/frames
User File Bit Order (LSB and MSB)
The signal generator views the data from the most significant bit (MSB) to the least significant bit
(LSB). When you create your user file data, it is important that you organize the data in this manner.
Within groups (strings) of bits, a bit’s value (significance) is determined by its location in the string.
The following shows an example of this order using two bytes.
Bit File Type Data
The bit file is the preferred file type and the easiest to use. When you download a bit file, you
designate how many bits in the file the signal generator can modulate onto the signal. During the file
download, the signal generator adds a 10–byte file header that contains the information on the
number of bits the signal generator is to use.
Although you download the data in bytes, when the signal generator uses the data, it recognizes only
the bits of interest that you designate in the SCPI command and ignores the remaining bits. This
provides greater flexibility in designing a data pattern without the concern of using an even number
of bytes as is needed with the binary file data format. The following figure illustrates this concept.
The example in the figure shows the bit data SCPI command formatted to download three bytes of
data, but only 23 bits of the three bytes are designated as the bits of interest. (For more information
Most Significant Bit (MSB) This bit has the highest value (greatest weight) and is located at
the far left of the bit string.
Least Significant Bit (LSB) This bit has the lowest value (bit position zero) and is located at
the far right of the bit string.
1 0 1 1 0 1 1 1 1 1 1 0 1 0 0 1
LSBMSB
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Data
Bit Position