User guide

Chapter 6. Following 207
Master Cycle Concept
Ratio Following can also address applications that require precise programming
synchronization between moves and I/O control based on master positions or external
conditions. The concept of the master cycle greatly simplifies the required synchronization.
A master cycle is simply an amount of master travel over which one or more related slave
events take place. The distance traveled by the master in a master cycle is called the master
cycle length. A master cycle position is the master position relative to the start of the current
master cycle. The value of master cycle position increases as positive-direction master cycle
counts are received, until it reaches the value specified for master cycle length. At that point,
the master cycle position becomes zero, and the master cycle number is incremented by one—
this condition is called rollover.
The master cycle concept is analogous to minutes and hours on a clock. If the master cycle is
considered an hour, then the master cycle length is 60 minutes. The number of minutes past
the hour is the master cycle position, and current hour is the master cycle number. In this
analogy, the master cycle position decrements from 59 to zero as the hour increases by one.
By specifying a master cycle length, periodic actions may be programmed in a loop or with
subroutines which refer to cycle positions, even though the master may be running
continuously. To accommodate applications where the feed of the product is random, the start
of the master cycle may be defined with trigger inputs. Two types of waits are also
programmable to allow suspension of program operation or slave moves based on master
positions or external conditions.
Master Cycle Commands
Following Status (TFSF, TFS and FS) bits 13-16 indicate the status of master cycle
counting. If a following application is taking advantage of master cycle counting, these bits
provide a quick summary of some important master cycle information:
Bit # Function (YES = 1; NO = Ø)
13 Master Cyc Trig Pend....... A master cycle restart is pending the occurrence of the specified trigger.
14 Mas Cyc Len Given........... A non-zero master cycle length has been specified with the FMCLEN
command.
15 Master Cyc Pos Neg......... The current master cycle position (PMAS) is negative. This could be by
caused by a negative initial master cycle position (FMCP), or if the master
is moving in the negative direction.
16 Master Cyc Num > 0........ The master position (PMAS) has exceeded the master cycle length
(FMCLEN) at least once, causing the master cycle number (NMCY) to
increment.
Master Cycle Length
(FMCLEN)
The FMCLEN command is used to define the length of the master cycle. The value entered
with this command is scaled by the SCLMAS parameter to allow specification of the master
cycle length in user units. This parameter must be defined before those commands which wait
for periodically repeating master positions are executed.
The default value of FMCLEN is zero, which means the master cycle length is practically
infinite (i.e., 4,294,967,246 steps, after scaling). If a value of zero is chosen, the master cycle
position will keep increasing until this very high value is exceeded or a new cycle is defined
with the FMCNEW command (or triggered after a TRGFNcx1 command) described below. If a
non-zero value for FMCLEN is chosen, the internally maintained master cycle position will
keep increasing until it reaches the value of FMCLEN. At this point, it immediately rolls over
to zero and continues to count.
The master cycle length may be changed with the FMCLEN command even after a master cycle
has been started. The new master cycle length takes affect as soon as it is issued. If the new
master cycle length is greater than the current master cycle position, the cycle position will
not change, but will rollover when the new master cycle length is reached. If the new master