Siemens SINUMERIK 840Di Function Manual page 789

2.4.6.3 Channel basic frames $P_CHBFR[n]
The number of basic frames can be configured in the channel via machine data
MD28081 $MC_MM_NUM_BASE_FRAMES.
The minimum configuration is designed for at least one basic frame per channel. A maximum
of 16 basic frames per channel is possible. In addition to the 16 basic frames, there can also
be 16 NCU-global basic frames in the channel.
System variable $P_CHBFR[n] can be used to read and write the basic frame field elements.
The chained complete basic frame is not activated simultaneously when writing a basic
frame field element, but rather activation only takes place on execution of a G500,G54, to
G599 instruction. The variable is used primarily for storing write operations to the basic frame
from HMI or PLC. These frame variables are saved by the data backup.
Current channel basic frames $P_CHBFRAME[n]
System variable $P_CHBFRAME[n] can be used to read and write the current channel basic
frame field elements. The resulting total 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.
Basic frame in channel $P_UBFR
The system variable is retained for reasons of compatibility, although it is redundant for the
$P_CHBFR[0] variables.
The basic frame with field device 0 is not activated simultaneously when writing to the
predefined $P_UBFR variable, but rather activation only takes place on execution of a
G500,G54, to G599 instruction. For NCU global frames, the changed frame only becomes
active in those channels of the NCU, which execute a G500,G54 to G599 instruction. The
variable is used primarily for storing write operations to the basic frame from HMI or PLC.
The variable can also be read and written in the program.
$P_UBFR is identical to $P_CHBFR[0]. One basic frame always exists in the channel by
default, so that the system variable is compatible with older versions. If there is no channel-
specific basic frame, an alarm is issued at read/write: "Frame: Instruction not allowed" is
output on a read or write access.
Current first basic frame in the channel $P_BFRAME
The system variable is retained for reasons of compatibility, although it is redundant for the
$P_CHBFRAME[0] variables.
The predefined frame variable $P_BFRAME can be used to read and write the current basic
frame with the field device of 0, which is valid in the channel, in the part program. The written
basic frame is immediately included in the calculation. In the case of NCU global settable
frames, the modified frame acts only in the channel in which the frame was programmed. If
the frame is to be modified for all channels of an NCU, $P_UBFR and $P_BFRAME must be
written simultaneously. The other channels must then activate the corresponding frame, e.g.,
with G54.
$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 allowed" is output on a read or write access.
Axis Types, Coordinate Systems, Frames (K2)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
Detailed Description
2.4 Frames
2-59