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e. Repeat steps c and d, substituting the full scale output value (20.0
mA) for the zero scale output value and the "TMX" command for
the "TMN" command.
Example: Enter "$1AO+00020.00"-output value is measured as
19.85 mA
Enter "$1WE"
Enter "$1TMX+00019.85"
Check revised output value, repeat if necessary.
f. It may be desirable to re-check the calibration of the zero-scale out-
put after adjusting the full-scale output.
NOTE. The DGH modules are rated for 12-bit precision, or 1 part in 4096,
while the command used to program their output has a resolution of 0.01
mA, or 1 part in 1600. The accuracy of the actual data being represented
by the analog output will typically be no better than 1-2% of the current
reading. At a reading equivalent to 10% of full scale, this equates to
approximately +/- 0.016 to 0.032 mA. Thus, extreme precision in
calibration of the DGH modules is generally not warranted.
E-4
Programming the Micro-Controller
The micro-controller currently used in the ADFM Analog Output Module is
the Parallax Basic Stamp IISX (BS2). This micro-controller is programmed
is the Parallax PBASIC2 variant of the BASIC programming language.
Operation of the module is controlled by the loaded BS2 program code, and
in-circuit reprogramming can be accomplished at any time. Additional in-
formation on the BS2 micro-controller can be obtained from the Parallax
web site, www.parallaxinc.com. Also available from their web site are pro-
gramming tools for both DOS and Windows, PBASIC reference guides,
software and hardware manuals, and links to other resources and reference
materials.
Initial programming for each unit will normally be provided by MGD Tech-
nologies Inc. based on the configuration of the system, the desired user
units, and the output scaling provided by the customer. The programmabil-
ity of the unit adds both power and complexity to the system; revision of
the programming apart from input parameter changes is not recommended
unless the user has experience with BASIC programming, using a very lim-
ited number of variables, and is familiar with the principles of 16-bit un-
signed integer mathematics.
ADFM Technical Manual (January 2000)
ADFM Analog Output Module
page E-9
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