Siemens SINUMERIK 840D sl Function Manual page 704

Measurement (M5)
Axial measurement (optional)
The values can be read from the FIFO both in the part program and from synchronized
actions.
The measurement is active until
● MEAC["axis"]=(0) is programmed,
● a FIFO is full,
● RESET is pressed or end of program M02/M30 is detected.
Endless measuring
In order to implement endless measuring, FIFO values must be read cyclically from the part
program. The frequency with which the measured values are read from the FIFO memory
and processed must correspond to the writing frequency of the NC.
The number of valid entries is readable in a FIFO variable.
In order to achieve a defined number of measured values, the measurement function must
be explicitly deselected by the program.
FIFO variables
For definitions of FIFO variables, see
References:
/FB2/ Function Manual Extended Functions; Synchronized Actions (S5)
704
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Extended Functions