Siemens SINUMERIK 840D sl Function Manual page 164

Several Operator Panels on Several NCUs, Distributed Systems (B3)
2.8 Cross-NCU user communication, link variables
Structure
Each NCU connected to an entire system with link module sees a link memory in which the
link variables are stored uniformly. Data exchange takes place after changes in the following
interpolation cycle.
Size of link memory
The size of the link memory can be configured within the limits set by machine data:
MD18700 $MN_MM_SIZEOF_LINKVAR_DATA
It is necessary to define the same size for all connected NCUs. If there are deviations, the
system adapts the link memory size of all NCUs according to the largest size specified. If the
memory area of the link memory is exceeded during an access attempt, alarm 17020 is
output.
Initialization of link memory
After power up, the link memory is initialized with 0.
Data types of link variables
The link memory can contain link variables with the following data types:
● INT $A_DLB[i] ; DataByte (8 bits)
● INT $A_DLW[i] ; DataWord (16 bits)
● INT $A_DLD[i] ; DataDoubleword (32 bits)
● REAL $A_DLR[i] ; Real data (64 bits)
Depending on the data type, 1, 2, 4, 8 bytes are addressed when reading/writing the link
variables.
The position offset in bytes in the data area for global data is determined directly by the
programmed field index. This is thus independent of the data type and specifies the offset in
bytes.
Ranges of values
The data types have the following value ranges:
BYTE: -128 to 255
WORD: -32768 to 65535
DWORD: -2147483648 to 2147483647
REAL: -4.19e
Alarm 17080 is generated when the upper value range limit is violated and alarm 17090 with
violation of the lower value range limit and alarm 14096 in the case of an illegal type
conversion.
The value range of these variables (with a negative value) applies only to write operations.
Only the corresponding positive (unsigned) value can be read back.
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Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Extended Functions