Siemens SINUMERIK 840D sl Programming Manual page 632

Work preparation
3.8 Coordinate transformations (frames)
Figure 3-2
If one of the following frames $P_BFRAME / $P_CHBFRAME[<n>], $P_IFRAME or $P_PFRAME
is changed, the current total frame $P_ACTFRAME is recalculated.
Basic frame and settable frame are effective after Reset if MD 20110 RESET_MODE_MASK
is set as follows:
Bit0=1, bit14=1 --> $P_UBFR (basic frame) acts
Bit0=1, bit5=1 --> $P_UIFR [$P_UIFRNUM](settable frame) acts
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Frame variable $P_ACTFRAME
Programming Manual, 12/2019, 6FC5398-2EP40-0BA0
NC programming