Fifo Variables (Circulating Memory) - Siemens SINUMERIK 840Di sl Function Manual

Detailed description
2.3 Special real-time variables for synchronized actions
2.3.6

FIFO variables (circulating memory)

Application
Up to 10 FIFO variables are provided to allow storage of related data sequences:
$AC_FIFO1[n] to $AC_FIFO10[n].
Structure
The memory structure of a FIFO-variable is shown in the figure: Example of FIFO variable
Amount
The number of the available AC FIFO variable is specified in machine data
MD28260 $MC_NUM_AC_FIFO
Size
The number of values that can be stored in a FIFO variable is defined via machine data
MD28264 $MC_LEN_AC_FIFO
All FIFO variables have the same length.
Data type:
Values in the FIFO-variables have the data type REAL.
Meaning of index
Index n:
Indices 0 to 5 have special meanings:
n=0: When writing with index 0 a new value is stored in the FIFO. When reading with index 0
the oldest element is read and deleted from the FIFO.
n=1: Access to oldest stored element
n=2: Access to latest stored element
n=3: Sum of all FIFO elements
The MD28266 $MC_MODE_AC_FIFO determines the mode
the summation:
Bit 0 = 1 sum upon each writing
Updating
Bit 0 = 0 no summation possible. n=4: Number of elements available in FIFO. Read and
write access can be assigned to each element of the FIFO.
FIFO variables are reset by resetting the number of elements, e.g. for the first FIFO variable:
$AC_FIFO1[0]=0
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Function Manual, 11/2006, 6FC5397-5BP10-2BA0
Synchronized actions