Siemens SINUMERIK 840D sl Function Manual page 33

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References
List Manual, System Variables
Synchronized actions
Function Manual, 08/2018, 6FC5397-5BP40-6BA2
Index of the FIFO variables with which the various functions and data within the data
structure of the FIFO variables is accessed.
Value range: 0, 1, 2, ... (MD28264 $MC_LEN_AC_FIFO - 1)
Value Meaning
0 Write
A value is written to the FIFO stack by assigning a value to the FIFO stack
via index 0 ($AC_FIFO[ 0 ] = <value>). The assigned value is written to the
next free location in the FIFO stack.
If all memory locations in the FIFO stack are already occupied, an alarm is
displayed:
● When writing in an NC program: Alarm 20149
● When writing in a synchronized action: Alarm 17020
Read
A value is read from the FIFO stack by assigning the FIFO stack to a variable
with index 0 (<variable> = $AC_FIFO[ 0 ]). The oldest value is read and then
removed from the FIFO stack.
Note
● Reading in the NC program / synchronized action
If a value is read in an NC program / synchronized action with index 0,
the oldest value is read and removed from the FIFO stack as described
above.
● Reading on the user interface, e.g. SINUMERIK Operate
If a value is read or displayed with index 0 on the user interface, e.g.
SINUMERIK Operate: "Diagnosis" > "NC/PLC Variables", the value is
read internally with index 1 (oldest value) without changing the FIFO
stack.
1 Write / Read: The "oldest" user data is addressed; the FIFO stack is not
changed
2 Write / Read: The "newest" user data is addressed; the FIFO stack is not
changed
3 Read: Returns the sum of the values of all user data
Enable via MD28266 $MC_MODE_AC_FIFO, bit 0 required. See paragraph
below "Summation across all user data"
4 Read: Supplies the number of user data currently stored in the FIFO stack.
Write: Reset to the initial state is realized by writing the value of 0 to FIFO
variable, index 4.
Example: $AC_FIFO1[4] = 0
5 Read: Returns the current write index, relative to the beginning of the FIFO
stack
6 Write/read: The 1st field element of the user data range is addressed
7 Write/read: The 2nd field element of the user data range is addressed
n Write/read: The nth field element of the user data range is addressed
3.3 System variables for synchronized actions
Administrative data
User data
Detailed description
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