DL205 Analog Manual, 7th Edition Rev. D
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Chapter 6: F2-04RTD 4-Channel RTD Input
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Writing the Control Program
Reading Values Pointer Method and Multiplexing
There are two methods of reading values:
•
Pointer method
• Multiplexing
The multiplexing method must be used with a DL230 CPU. The multiplexing method must
also be used with remote I/O modules (the pointer method will not work). Either method can
be used with the DL240, DL250-1 and DL260 CPUs, but for ease of programming it is highly
recommended to use the pointer method.
Pointer Method for the DL240/250-1/260 CPUs
The CPU has special V-memory locations assigned to each base slot that greatly simplifies the
programming requirements. These V-memory locations:
•
Specify the number of channels to scan.
•
Specify the storage locations.
The example program shows how to setup these locations. Place this rung anywhere in the
ladder program, or in the initial stage if stage programming instructions are used. This is all
that is required to read the data into V-memory locations. Once the data is in V-memory, math
instructions can be used on the data, compare the data against preset values, etc. V2000 is used
in the example, but any user V-memory location can be used. The module is installed in slot 2
for the examples. Use the V-memory locations shown in the application. The pointer method
automatically converts values to BCD.
NOTE:
DL240 CPUs with firmware release version 2.5 or later and DL250 CPUs with firmware release version 1.06 or later
support this method. Use the DL230 multiplexing example if the firmware revision is earlier .
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SP0
LD
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LDA
O2000
OUT
V7672
This loads an octal value for the first V-memory location that will be
used to store the incoming data. For example, the O2000 entered
here would designate the following addresses:
Ch1 -- V2000, V2001, Ch 2 -- V2002, V2003, Ch 3 -- V2004, V2005,
Ch 4 -- V2006, V2007.
The octal address (O2000) is stored here. V7672 is assigned to slot
2 and acts as a pointer, which means the CPU will use the octal
value in this location to determine exactly where to store the
incoming data.
OUT
V7662
Special V-memory location assigned to slot 2 that contains the
number of channels to scan.
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LD
Loads a constant that specifies the number of channels to scan and
the data format. The upper byte, most significant nibble (MSN)
selects the data format (0=BCD, 8=Binary), the LSN selects the
number of channels (1, 2, 3, or 4).
- or -
The binary format is used for displaying data on some operator
interfaces. The DL230/240 CPUs do not support binary math
functions, whereas the DL250 does.
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K
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Содержание DL205
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