<9. Advanced Engineering >
9.2.5 Selection of Timers and Counters
When creating logic related to elapsed time for FCN-500 or FCN-RTU, either a timer
function block or the NPAS_TM POU can be used.
When creating logic related to counting, either a counter function block or the
NPAS_CT POU can be used.
• Timer function blocks
TP : Pulse
TON : On-delay timer
TOF : Off-delay timer
Use these timer function blocks for programming simple pulse generation, on-
delay or off-delay logic.
• Counter function blocks
CTU : Up-counter
CTD : Down-counter
CTUD : Up-down counter
Use these counter function blocks for programming simple counting logic.
NPAS_TM and NPAS_CT POUs, which are included in NPAS_POU, provide the
following additional functions over the timer/counter function blocks:
- Suspend/resume timer or counter
- Modify current timer/counter value
Moreover, NPAS_TM and NPAS_CT include access parameters for the preset and
current counter/timer values. As described in Section 9.1.9, “Specifying Retain Data
and OPC Property,” access parameters are specified as retain data and specified
with OPC property within the system.
To summarize, use NPAS_TM or NPAS_CT in logic related to elapse time or
counting when there is a need to suspend/resume the timer/counter, or modify the
current timer/counter value, or set OPC property of timer/counter values.
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