Siemens SINUMERIK 840D sl Function Manual page 637

Main block
All instructions required for processing the subsequent section of the part program must be
programmed in one main block.
The main blocks are to be designated with a Main Block No. consisting of the sign ":" and a
positive whole number (block number).
References:
/PG/ Programming Fundamentals Manual; Fundamentals of NC Programming, Language
Elements of the Programming Language
Activation
Activation of the block search from the last main block is performed using the RESU-specific
machine data:
MD62575 $MC_RESU_SPECIAL_FEATURE_MASK_2, bit 0 (additional RESU features)
Bit
0
Constraints
In order that a new retrace support operation can take place following a retrace support
operation with block search from last main block, the RESU start CC_PREPRE(1) must be
programmed in the retrace support ASUB "CC_RESU_BS_ASUP.SPF".
Programming example:
PROC CC_RESU_BS_ASUP SAVE
M17
Special Functions
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
Value Meaning
0 Retrace support is performed using block search with calculation on contour.
1 Retrace support is performed using block search from the last main block.
; (synchronized actions, M functions, etc. required for retrace support
)
CC_PREPRE(1)
RMN
REPOSA
TE7: Continue machining - retrace support
15.6 Retrace support
637