Rockwell-automation 1771-DMC_DMC1_DMC4_DXPS Control Coprocessor User M Manual de usuario descargar pdf (Pagina 248)

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Appendix B



B-117

Returns

Value Symbolic Name Meaning

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Description

Use TAG_DEFINE to place a TAG name entry into the TAG table. The

TAG name is a symbolic reference to the user’s designated data area. The

TAG_DEFINE routine also returns a handle with which the calling task

can refer to the TAG area on subsequent TAG_ calls. This handle is an

offset into the TAG table. This makes subsequent access to the table faster

than doing a symbolic name search.

When a process defines a TAG name, a pointer referencing the tagged

memory is stored in the TAG table. If the process that defined the TAG

aborts or is terminated, the memory referenced by the TAG pointer is

returned to the free memory pool. The TAG pointer still exists in the TAG

table, but that memory no longer addresses the TAG and may contain

invalid data.

ATTENTION: A process that creates any TAG

must not terminate if that TAG is to remain valid.

To correctly remove a TAG, use the TAG_UNDEF

or TAG_GLOBAL_UNDEF function or reset the

coprocessor module.

C Example

unsigned off;

unsigned fred;

unsigned status;

status = TAG_DEFINE

(&off,&fred,“Fred”,sizeof(fred),TG_MODIFY);

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Rockwell-automation 1771-DMC_DMC1_DMC4_DXPS Control Coprocessor User M Manual de usuario Pagina 248