Synchronization Of A Write Request; Example: Structure Of The Link Variables Memory - Siemens SINUMERIK 840D sl Function Manual

3.2.2.6

Synchronization of a write request

If certain applications require the new value of a link variable to be transferred to the other
NCUs in the link group in precisely two interpolation cycles, writing to the link variable must be
made in a synchronized action. In the synchronized action, writing to the link variable is only
executed if in the actual interpolator cycle, the write request can still be executed. The
$A_LINK_TRANS_RATE system variable contains the number of write requests that can still
be transferred in the current interpolator cycle.
In the following example, a link variable, data type WORD (2 bytes) and a link variable, data
type DWORD (4 bytes), are written:
Program example
N120 WHEN $A_LINK_TRANS_RATE > 0 DO $A_DLW[0] = 9
N125 WHEN $A_LINK_TRANS_RATE > 0 DO $A_DLD[2] = 7
N130 G4 F1
The synchronized action in N120 is performed only when the write request can be transferred
in the same interpolator cycle to the other NCU of the link group. In this case, the
$A_LINK_TRANS_RATE system variable is also decremented in the same interpolator cycle
so that the updated value is available for the synchronized action in the following N125 block.
3.2.2.7

Example: Structure of the link variables memory

The following data are defined for the link communication:
Data format
BYTE
WORD
DWORD
REAL
required size of the link variables memory:
Memory structure
The data is arranged in the link variables memory as follows, with the data format limits taken
into account:
Extended Functions
Function Manual, 10/2015, 6FC5397-1BP40-5BA3
Number Bytes per data
2 1
1 2
3 4
1 8
B3: Distributed systems - 840D sl only
Bytes required
2
2
12
8
24
3.2 NCU link
95