The Arc Absolute Instruction, Aa - HP 7470A Interfacing And Programming Manual

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Lines 20 and 30 define the plotting area and perform user-unit scaling.
Line 40 moves the pen to point (—800,800) to locate the starting point of
the first pattern.
Lines 130 and 140 contain the subroutine necessary to draw the
pattern. First, a 50-unit radius circle is drawn, followed by a relative
move of 600 units in the X-direction where another 50-unit radius
circle is drawn. A move of -300 units in X and -300 units in Y
locates the center of the 250-unit circle. The last two 50-unit circles
are drawn with the moves shown in the listing.
Lines 60, 80, and 100 locate the starting points of the other three
patterns.
START
PA (-800,8001
PA (200,800)
PA (-800,-200)
PA (200.-200)
3-16 CONTROLLING THE PEN AND PLOTTING
V )
The Arc Absolute Instruction, AA
The arc absolute instruction, AA, provides the means
to draw an arc with the center point located at a specified absolute
point. The arc can be drawn clockwise (CW) or counterclockwise (CCW),
subtends the specified arc angle, and conforms to the specified or
default chord angle. It is only included in the instruction set of RS-232-C
plotters that have the serial prefix number 2308A or higher.
I I M y l The instruction can be used to draw an arc of any radius,
length, and smoothness with a single command. The arc is drawn from
the current pen position, and its center point is located by absolute X,Y
coordinates.
Bina
^ ~
U ARC AN
AA
3LE
X-coordinate, Y-coordinate, arc angle
terminator
CURRENT PEN
POSITION
CHORD
ANGLE
V ABSOLUTE X , Y
~?* COORDINATES
(ARC CENTER)
ABSOLUTE
COORDINATES (AR
ARC ANGLE / \
A N G L E -
(, chord angle)
K.Y
C CENTER)
, * f * \ CURRENT
i f ^ ^ P E N
l A j £ ^ POSITION
I
EXPLANATION
The AA instruction requires that both X- and Y-
coordinates be specified (coordinate pair) in integer format. They are
interpreted as plotter units if scaling is off or as user units if scaling is
on. The X- and Y-coordinates locate the center of the arc and may be
located on or off the plotting surface. The current pen position is the
starting point of the arc.
The arc angle is in integer format. It is the angle, in degrees, through
which the arc is drawn: a positive arc angle draws CCW from the
current pen position; a negative arc angle draws CW from the current
pen position.
The chord angle parameter is in integer format and governs the
smoothness of the arc in the same way as defined under the circle
instruction, CI. The sign of the parameter is ignored, except to set the
maximum in-range limit to - 3 2 768 or +32 767. The default chord angle
is 5 degrees.
Unlike circles, arcs are drawn using the previously commanded pen
state (up or down) and line type. If no pen state has been commanded
CONTROLLING THE PEN AND PLOTTING 3-17