Siemens sinumerik 840d Programming Manual page 214

Frames
6
6.9 NCU-global frames (SW 5 and higher)
840D 840D
NCU 571 NCU 572
NCU 573
$P_CHBFR[n]
The base frames can be read and written via system
variable $P_CHBFR[n]. When writing a base frame,
the chained total base frame is not activated; it is
only activated when the G500, G54..G599 instruction
is executed. The variable mainly serves as memory
for writing processes to the MMC and PLC base
frame. These frame variables are saved by data
backup.
First base frame in the channel
Writing on the predefined variable $P_UBFR does
not cause the base frame with array index 0 to be
activated at the same time, rather activation occurs
only when a G500, G54..G599 instruction is
executed. The variable can also be written and read
in the program.
$P_UBFR
$P_UBFR is identical to $P_CHBFR[0].
As standard, there is always a base frame in the
channel making the system variable compatible with
older versions. If there is no channel-specific base
frame, an alarm is issued at read/write: "Frame:
instruction not permissible".
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FM-NC 810D 840Di
SINUMERIK 840D/840Di/810D/FM-NC Programming Guide Advanced (PGA) − 04.00 Edition
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