Rockwell-automation 1771-DMC_DMC1_DMC4_DXPS Control Coprocessor User M Manual do Utilizador descarregar pdf (Página 104)

Chapter 6

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6-23

All external access to the control coprocessor’s user memory is through the

TAG table of the coprocessor. The TAG functions provide a way for you

to specify access to control-coprocessor memory. The memory of the

tagged area can be of any data type—e.g., char, short, float, etc.—or

combination of data types. It is your responsibility to understand the

layout of the tagged memory. Transmission or reception of tagged

memory data is done as a “byte stream.” External devices can have

different memory structures—i.e., byte order, data sizes, etc. When

reading tagged data from the coprocessor, the external process must

accommodate the differences when interpreting the byte stream. Similarly,

when writing to the tagged area, the external process must generate a byte

stream to match that of the coprocessor tagged memory.

EXAMPLE Program of INTERCHANGE Access

to CoprocessorĆTagged Memory

The following example illustrates how to set up the tagged memory of the

coprocessor and access that memory over Ethernet using INTERCHANGE

software on the host computer.

In this example, we set up a tagged area defined by the structure CAR.

The TAG name “Car” points to the start of the CAR structure. The

memory allocated by the OS9 compiler for the CAR structure is:

Structure Offset Allocation

 *  ! '& *

 ! '& *

 ! '& *

 ! '& *

 !#

 '($

 # #%

 )$ ('

 (% '& *

 (% '& *

 (% '& *

 (% '& *

Note the inclusion of a “pad” byte generated by the compiler. The pad

byte is necessary to make year start on an even addressed boundary. This

illustrates how imperative it is that you know the exact memory layout of

the tagged area.

The following example of a coprocessor program creates the Car TAG and

periodically increments the make, model and type elements of the

structure. In this example, the coprocessor is set up to be station 22 octal

(12h). To increase readability of the example, no error checking is done.

1 2 ... 99 100 101 102 103 104 105 106 107 108 109 ... 311 312

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