Siemens SINUMERIK 840D sl Programming Manual page 295

$P_CHBFRAME[n] Current channel basic frames
System variable $P_CHBFRAME[n] can be used to read and write the current channel basic
frame field elements. The resulting complete basic frame is calculated by means of the write
process in the channel. Whenever a basic frame is written, the complete basic frame is
calculated again.
$P_BFRAME Current first basic frame in the channel
The predefined frame variable $P_BFRAME can be used to read and write the current basic
frame with the array index 0, which is valid in the channel, in the part program. The written
basic frame is immediately included in the calculation.
$P_BFRAME is identical to $P_CHBFRAME[0]. The system variable always has a valid
default value. If there is no channel-specific basic frame, an alarm is issued at read/write:
"Frame: instruction not permissible".
$P_ACTBFRAME Complete basic frame
The $P_ACTFRAME variable determines the chained complete basic frame. The variable is
read-only.
$P_ACTFRAME corresponds to:
$P_NCBFRAME[0] : ... : $P_NCBFRAME[n] : $P_CHBFRAME[0] : ... : $P_CHBFRAME[n].
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Programming Manual, 03/2013, 6FC5398-2BP40-3BA1
Coordinate transformations (frames)
5.7 NCU global frames
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