Siemens SIMATIC S7-300 Manual page 265

Notes to the exam- The axis travels until a signal change from 0 to 1 takes place at the digital
ple of external
input. This triggers two reactions:
block change
Depending on the situation, N20 is processed as follows:
If no signal change occurs at the digital input, the target position of N10 is
approached, with the following additional response:
When the target position is reached, the error message "Digital input not ac-
tuated" is output (see Table 11-5, Class 2 No. 15).
Set actual value The "Set actual value on-the-fly" function is programmed and triggered by a
on-the-fly G87, digital input; the block change occurs on the fly and the actual value is set to
G88, G89 a new dimension (programmed coordinate) at the same time. The digital in-
put must be parameterized with the "Set actual value on-the-fly" function by
way of machine data item MD34.
FM 354 Servo Drive Positioning Module
A block change on-the-fly, and thus immediate processing of block N20.
Storage of the actual position at the time of this signal change to "Actual
value block change." This position is also the starting position for any
subsequent chain-measure programming.
If the block position in N20 is less than the actual position at the time
when the digital input is received (reversal of direction), the equipment is
stopped so that the position can then be approached in the opposite direc-
tion.
If no position is programmed in block N20, movement is braked, the
functions programmed in N20 are executed, and processing then moves
on to the next block (except if the block contains M0, M2 or M30).
If the programmed path in block N20 is less than the deceleration dis-
tance, the programmed position is overshot and then positioned by a re-
versal of direction.
Writing Traversing Programs
10-5