NI PXI-7340 Programmable power supply

A limited memory area is reserved for each user cycle level and for levels containing RESTART or operator input programs. This memory area is used for storing the currently utilized variables (stack). These auxiliary cells should be assigned sequentially starting with 0. A stack overflow and fatal consequences may result if this has not been observed and several nestings have been used. (System performs a restart).The following example shows the amount of space required by a user program with the variable numbers selected and a nesting depth of 2.

The auxiliary cells used for the execution of PROBLEM.

A thus occupy 996 bytes. If numbering of the variables of each program in this example started from 0, the system would only have to reserve 96 bytes. The above calculation gives only a rough estimate as the system requires additional space in the stack (cf. error numbers S358 and S359). The contents of the auxiliary cells is only defined uniquely if it has been loaded/described in the block. The program is aborted and error number S 302 issued if an LA/LB variable is accessed which has not been parameterized previously. The meaning of the auxiliary cells lost as soon as the last instruction of the block has been executed. They are not suitable for storing values which are to be saved over several cyclic block executions (this function is performed by GA/GB/GM/GT data blocks).

Remedy in the case of a stack area overflow

The second I&C alarm indicates (with cycles 1 to 5) the block installed in the cycle. If there is a stack overflow upon a standard operation, a system block is indicated as installed block. The alarm S358 means that there is not enough free stack area left for calling a subroutine. The called subroutine needs more stack area for execution (too many LA/LB variables). The line number of the calling program is displayed with the extended output of I&C alarms.

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