Programming Elements and Sequential Order of Programming
1. Logic controlling the enable input from the left bus. Must start with an LD element.
2. Type of function (Function 14)
3. Parameter (P1) Timer Accuracy or base value for timing increments;
1 = one hundredth of a second (.01 second),
10 = one tenth of a second (0.1 second).
4. Parameter (P2) Preset Time, a constant number or the register that will contain the
5. Parameter (P3) Timer Location, the first register of the three sequential registers con-
taining the operating values.
Parameters for OFDTR (Function 14)
The following table specifies which memory types are valid for each of the OFDTR func-
tion block’s parameters:
Important Product Information
Allowable Memory Types for OFDTR (Function 14)
Timer Accuracy (P1)
Preset Time (P2)
Timer Location (P3)
Timer Accuracy (P1):
The timer accuracy parameter indicates the time base of the timer.
A constant of 1 indicates a time base of 0.01 second; 10 indicates a time base of 0.1 se-
conds. Other values are not accepted as a valid parameter value.
Preset Time (P2):
The preset time parameter indicates the time period for the off-delay
timer. It is indicated by a positive (only) 16-bit twos complement signed integer
(0...32,767). A constant of -1 indicates that no preset time parameter is specified. For this
case, the preset time will be accessed from the Operating Registers of the timer.
Timer Location (P3):
The timer location gives the address of a three-word data structure
which is used by the timer function block.
Programming Example for OFDTR Function
In the following example, power flow will be passed through the OFDTR to turn on
%Q0001 at a time of 2.5 seconds after input 1 goes from being closed to opened. The
Time Base or Timer Accuracy is a tenth of a second (.01); the Preset is a constant of 25,
and the Location of this OFDTR is Register 1.
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