Reading Plots from the Communication Module

Overview

To load all plots on eight axes, the user would need to reserve 49,152 PLC registers. A single-axis full plot requires 6,144 PLC registers. A plot of a single piece of information on one axis requires 1,024 PLC registers.

The chart below can be used to determine the start of a given plot. n represents the axis number (0-7). Remember that there are 1024 registers per plot, so for non-Allen-Bradley addressing, the 1024 sequential registers hold each sample, but for Allen-Bradley addressing, only 256 registers fit in a register file. Therefore, the first 256 samples are in the register file calculated by the table below as elements 0-255. The next 256 samples are in the next register file, and so on.

†See the sections below for details on these arrays.

Position Units

The positions returned in these arrays are not in position units. The numbers returned are unsigned 16-bit numbers. To convert a ”r;position” returned in the array, perform the following math:

Position_real = ( Position_plot x Sign ) + Offset

In this equation, Sign will be +1 if the Scale is positive and -1 if the Scale is negative. For best results, this equation should be worked out using 32-bit integers or floating point math.

Extra Plot Data

Refer to the Selecting the Data to Plot topic for details on selecting the data to be entered into the last two plot arrays. The exact formats of the plot arrays are described below:

• Extra Position Precision:
  When reading extra precision graphs, Extra Plot Data #1 gives the fractional portion of the Target Position, and Extra Plot Data #2 gives the fractional portion of the Actual Position.
  To calculate the fraction, treat the fraction as an unsigned 16-bit number, and divide it by 65536. Then, add this number (which will be less than one) to the raw Target and Actual Positions returned in the first two plot arrays.

Note: Add the fractions before converting the raw Target and Actual to final Target and Actual Positions are described in the section above.

• Command/Command Value:
  Extra Plot Data #1 gives the Command, and Extra Plot Data #2 gives the Command Value.

• Current Event/Link Value:
  Extra Plot Data #1 gives the Event Step, and Extra Plot Data #2 gives the Link Value.

• Raw Transducer Counts:
  Extra Plot Data #1 gives the low 16-bits of the Raw Transducer Counts. Extra Plot Data #2 gives the high 16-bits of the same internal register.

• Internal Speeds:
  Extra Plot Data #1 holds the Target Speed, and Extra Plot Data #2 holds the Actual Speed. Both are in position units per second.

• Integral Drive:
  Extra Plot Data #1 holds the Integral Drive in drive count units. There are 8192 drive count units in 10000 mV. Therefore a value of 819 is equal to 1000 mV. Extra Plot Data #2 holds the fractional part of the Integral Drive, where this register is the numerator and the denominator is 65,536. The fractional part can usually be ignored except when determining the rate the integral is winding up or down.

Auxiliary Axes

For auxiliary (non-position analog) axes, the Drive, Extra Plot Data #1, and Extra Plot Data #2 tables are unused. In addition, the target and actual analog values are signed 16-bit values that match the values displayed in RMCWin. Therefore, no conversions need to be done on them as must be done with position units. The following chart shows the starting addresses of each auxiliary axis’ 1024-element sample arrays:

Copyright (c) 1997-2015 by Delta Computer Systems, Inc.