A2: Various NC/PLC interface signals and functions
1.3 Functions
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
59
1.3.3 Activate DEFAULT memory
GUD start values
The DEF... / REDEF... NC commands can be used to assign default settings to global user data (GUD). These
default settings must be permanently stored in the system if they are to be available after certain system states
(e.g. RESET).
The memory space for this is taken from the memory area that was assigned via the machine data:
MD18150 $MM_GUD_VALUES_MEM (number of additional parameters according to MD18170)
The setting for activating the stored default values is made in machine data:
MD11270 $MN_DEFAULT_VALUES_MEM_MASK (activation default values for NC language elements)
References:
/FB1/Function Manual Basic functions; S7: "Memory Configuration"
/PGA/ Programming Guide Advanced
1.3.4 Read/write PLC variable
High-speed data channel
For highspeed exchange of information between the PLC and NC, a memory area is reserved in the
communications buffer on these modules (dualport RAM). Variables of any type (I/O, DB, DW, flags) may be
exchanged within this memory area.
The PLC accesses this memory using 'Function Calls' (FC) while the NCK uses '$ variables'.
Organization of memory area
The user's programming engineer (NCK and PLC) is responsible for organizing (structuring) this memory area.
Every storage position in the memory can be addressed provided that the limit is selected according to the
appropriate data format (i.e. a DWORD for a 4byte limit, a WORD for a 2byte limit, etc.).
The memory is accessed via the data type and the position offset within the memory area.
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