HP 8530A, Руководство по эксплуатации и программированию, Страница: 339 / 439

HP-IB Programming Basics
In F orm 4, This is an ASCII format, which contains only data blocks , each of which being 24
bytes long. Each of these blocks contain a data pair , in which the two numbers is separated by
a comma. Each block is separated by a line feed.
F orm 5, each block is 32 bits long (8 bytes per data point).
When the data transfer begins , HP B ASIC automatically reads the size information in the Size
Block, and transfers the data accordingly . Other languages require the user to dene these
block sizes ahead of time , usually when the I/O path is dened.
Setting Up V ariables
Unless you are using F orm 4, you must set up an integer variable for the preamble and the Size
Block. Dimension an array of appropriate size for the data. F orm 4 data requires a string array .
Dynamic Array Allocation
Setting up xed array sizes is all you may need in simple programs . However , large
measurement programs may need to call subroutines that can intelligently determine the size of
the required data array . F ortunately , you can write your program so it reads the Size Block and
then dynamically allocates the required data array storage , as in this sequence:
ENTER Rec_Data;Preamble, Size
N=Size/16 ! 16 bytes per data point using Form 3
REDIM Data(1:N, 1:2)
OUTPUT Rec;"FORM3;OUTPDATA;"
ENTER Rec_Data; Data(*)
Y ou can do the same thing in Frequency Domain by making the number of points the active
function then reading the value , as in this sequence:
OUTPUT Rec; "POIN; OUTPACTI;"
ENTER Rec_Data; Points
REDIM Data(1:Points, 1:2)
OUTPUT Rec;"FORM3;OUTPDATA;"
ENTER Rec_Data; Preamble, Size, Data(*)
A similar method could be used for Angle Domain. In this case you can calculate the number
of data points by reading the start angle , stop angle , and increment angle . Y ou must make each
of these the active function before reading the value .
Note that all transfers use standard IEEE 728 block transfer formats with EOI asserted with
the last byte of data.
P erforming the A ctual Transfer
Now that you know which data array and transfer format to use , and have dimensioned
appropriate computer variables and an array , you are ready to perform the actual data transfer .
Example:
The following HP B ASIC example performs a data transfer , and demonstrates many
commonly-needed tasks , including:
Measurement setup
Data acquisition
Conversion of real and imaginary data into magnitude and phase format
Printout of the values for each point
This is a complete example . It dimensions all needed variables , shows all HP-IB bus
\maintenance" commands , and so on. If you are not using HP B ASIC you will have to write the
18-10 HP-IB Programming