Toshiba T2N - Manual (Page 120)

2.INTERNAL OPERATIONS
User’s manual 107
The constant scan mode has a specified time cycle for scanning. The set up
range of the cycle is 10 - 200ms (10ms units). Use this scan cycle to avoid
variation in scan intervals.
The action of the constant scan when the cycle is fixed at 50ms is shown in the
following diagram.
Scan mode selection is performed by setting up the scan cycle in the system
information menu of the programmer.
To select floating scan, do not set up a scan time (leave blank).
With the constant scan the scan time can be set up within the range 10 - 200ms
(10ms units).
Note) In the constant scan if the time for one scan is exceeded in a specified
cycle it becomes a floating scan, and the fixed time scan retard flag
(special relay - S0008) comes ON. Also, when the scan time reverts
to within the specified cycle the scan cycle returns to the original
constant scan.
scan cycle (fixed at 50ms)
mode I/O timer user program mode I/O timer user program
scan cycle (fixed at 50ms)
immediately to next can
mode I/O timer mode timer I/O user program mode user program
fixed time scan fixed time scan
returns to constant scan