Hardware Reference
In-Depth Information
acquisition which allows up to 2300 measurements per second), period (both
single and multiple), and time interval (i.e. the elapsed time between 'start' and
'stop' events). In addition, a direct data acquisition mode places measurements
into a memory array without the usual overheads required to communicate
results back to an application program via DOS).
The GT200 software is capable of performing a number of statistical
functions (including mean, standard deviation, maximum and minimum meas-
urements within a sample block). These are ideal for determining parameters,
such as drift and 'jitter'.
The GT200 measures input signal frequencies using the most accurate tech-
nique available, reciprocal counting coupled to time interpolation. There are two
primary benefits of this method: improved accuracy and reduced measurement
time. Fast measurements with high accuracy yield more information concern-
ing the stability of a signal. The GT200 is able to compute the drift rate, mean,
and peak-peak jitter of a signal in the same time interval that a conventional
counter is simply measuring frequency.
Software
The control program sends commands to the GT200 driver as character strings
through standard DOS file write operations. Several conventions must be obeyed
when incorporating commands into programs (e.g. individual commands must
be separated by semicolon, carriage return, or line feed delimiters). Com-
mands are not case sensitive and may be abbreviated for convenience. The
minimum acceptable abbreviations for each command are listed in the manual.
As an example, FREQ may be used instead of FREQUENCY, FU instead of
FUNCTION, and so on.
GT200 commands are incorporated in normal program statements, such as
BASIC:
PRINT#, "fu freqa; gate 0.01"
or in C:
fprintf(COUNTER, "fu freqa; gate 0.01");
A simple program, like the QBASIC program shown below, can be eas-
ily developed to meet the client's requirements for the long-term stability
measurement (involving 100 readings taken at 10-s intervals).
REM Oscillator test program
REM Declare sub-programs
DECLARE SUB max ()
DECLARE SUB min ()
DECLARE SUB mean ()
REM Dimension array for collected data
DIM freq(100)
REM Get oscillator reference
CLS
INPUT "Enter oscillator reference: "; ref$
LET ref$ = LEFT$ (ref$, 6)
