Chapter 4. Ladder Diagram (LD) Programming
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PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual
GFK-2950C
4.13.3
Standard Timer Function Blocks
The standard timers are a pulse timer (TP), an on-delay timer (TON), and an off-delay timer (TOF).
The pulse timer block can be used to generate output pulses of a given duration. The on-delay timer
can be used to delay setting an output ON for a fixed period after an input is set ON. The off-delay
timer can be used to delay setting an output OFF for a fixed period after an input goes OFF so that
the output is held on for a given period longer than the input.
Notes:
Any block type can contain calls to the standard timers. (See Chapter 2 for a discussion of the
various block types.)
Interrupt blocks can contain standard timers.
An instance of a timer can be passed by reference to a parameterized block or UDFB.
When the timer stops timing as a result of reaching its Preset Time (PT), the Elapsed Time (ET)
contains the actual timer duration. For example, if the Preset Time was specified as 333ms, but
the timer actually timed to 350ms, the 350ms value is saved in ET.
Data Required for Standard Timer Function Blocks
Each invocation of a timer has associated instance data that persists from one execution of the
timer to the next. Instance variables are automatically located in symbolic memory. (You cannot
specify an address.) You can specify a stored value for each element. The user logic cannot modify
the values.
Each timer instance variable has the following structure. Elements of a timer structure cannot be
published.
The instance data type for each timer must be the same as the timer type:
The TOF timer requires an instance variable of type TOF.
The TON timer requires an instance variable of type TON.
The TP timer requires an instance variable of type TP.
Element
Type
Description
Details
IN
BOOL
Timer input
Cannot be accessed in user logic.
PT
DINT
Preset time
Cannot be accessed in user logic.
ET
DINT
Elapsed time
Read only. Accessible in user logic.
Q
BOOL
Set ON when timer finishes timing
Read only. Accessible in user logic.
ENO
BOOL
Enable output
Read only. Accessible in user logic.
TI
BOOL
Set ON when the timer instance is timing
(that is, ET is incrementing).
Read only. Accessible in user logic.
Resetting the Timer
The preset time (PT) may be changed while the timer is timing to affect the duration.
When the timer reaches PT, the timer stops timing and the elapsed time parameter (ET) contains the
actual timer duration.
To reset the timer function block, set the PT input to 0. When the function block resets:
▪
ET is set to 0
▪
Q is set to off (0)
▪
The TI element is set to 0
▪
The IN parameter is ignored
Summary of Contents for PACSystems RX7i
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