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Restrictions on DLB Operation
Because DLBs are intended only for temporary use, there are more restrictions on their operation
compared to application logic blocks. All built-in functions and function blocks other than those
listed below can be used in DLB logic.
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DLB logic may not call any logic block or be called by any logic block.
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You cannot define parameters or scheduling for a DLB.
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A DLB has no parameters other than the standard ENO output parameter. Since DLBs cannot be
called from other blocks, you can access its ENO parameter only by reading or writing it in the
DLB's logic.
You cannot use variables that have %L or %P addresses. As a consequence, the following
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features that require %L or %P memory cannot be used in a DLB:
a. #FST_EXE system variable
b. The built-in timer function blocks, ONDTR, OFDT, and TMR
c. %L or %P variables.
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Locally scoped variables must be symbolic. For additional information, refer to DLB Variables.
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DLBs or their associated files cannot be loaded from the RX3i.
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DLBs and their associated files cannot be downloaded to flash memory.
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You cannot give an LD DLB the name _MAIN.
You cannot modify an active LD DLB while it is executing on the Controller.
▪
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You cannot perform a Test Edit (Online Edit Mode and Online Test Mode).
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You cannot perform word-for-word changes on an active DLB.
DLB Variables
A DLB can have its own variables, which are local to the DLB and not accessible by any other block.
All DLB local variables are symbolic, retentive, and published.
Local variables should be used within DLBs whenever possible. If the system is already running and
you create new global variables in the DLB, the programming software will not download the DLB
because the programmer's memory map will no longer match the RX3i controller's memory map.
DLB logic can read and write the global variables of the application that resides in the same target as
it does. These variables may be mapped or symbolic.
To use functions that require the use of located variables, a DLB must use the global located
variables of the application that resides in the same target as the DLB. These functions include:
a. COMMREQ (location of the Status variable)
b. DO_IO
c. Some SVC_REQ functions
A DLB can create aliases to global located application variables or arrays of variables that were
specifically created and documented to serve as scratchpad memory for DLBs that need to use
located variables.
GFK-2950C
February 2018
Chapter 9. Diagnostics
445
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