Yaskawa YASNAC PC NC PLC Programming Manual - Manual (Page 21)

4 - 4
YASNAC PCNC PLC Programming Manual Chapter 4: Sequence Control Method
(1) High-speed Processing Sequence Program
The high-speed processing sequence program, from the beginning of the sequence pro-
gram up to the RTH instruction, is executed once every setting scan time or less as shown in
the time charts above.
During the processing of the high-speed sequence program, the input status remains
unchanged.
The high-speed processing sequence program treats only the portion where high-speed
response is required, such as counting the contact ON/OFF.
Therefore, this should be limited only to the requisite program.The capacity must be less
than 1000 steps when converted into the contact instructions.
(2) Low-speed Processing Sequence Program
The low-speed processing sequence program entered following the RTH instruction is divided
into “n” sections and one of these sections is executed in the remaining time in each setting
interval. That is, the low-speed processing sequence program is executed once in “setting
scan time × n”.
Scan time of the low-speed processing sequence program is influenced by the total capacity
of the sequence program. As seen above, value “n” will be smaller as the total program capac-
ity and the high-speed processing program capacity are smaller.
For PCNC, NC service task takes priority. If the divided low-speed program is perform-ed in
the setting scan section, the remaining program will not be performed in the next section. The
execution of low-speed sequence program is determined by system soft-ware, which monitors
the load of entire system.
Sequence program size that can be processed in a 8-msec interval is approximately 6000 steps
in contact instructions. This size is the total of high-speed processing sequence program and
low-speed processing sequence program.