Function Block
A function block groups an algorithm and a set of private data. It has inputs and outputs. - Down counter.
Inputs
|
Input |
Data Type |
Range |
Unit |
Default |
Description |
|---|---|---|---|---|---|
|
CD |
BOOL |
|
|
|
Enable counting. Counter is decreased on each call when CD is TRUE. |
|
LOAD |
BOOL |
|
|
|
Re-load command. Counter is set to PV when called with LOAD to TRUE. |
|
PV |
DINT |
|
|
|
Programmed maximum value. |
Outputs
|
Output |
Data Type |
Range |
Unit |
Description |
|---|---|---|---|---|
|
CV |
DINT |
|
|
Current value of the counter. |
|
Q |
BOOL |
|
|
TRUE when counter is empty (i.e., when CV = 0). |
Remarks
- The counter is empty (CV = 0) when the application starts.
- The counter does not include a pulse detection for CD input.
- Use the R_TRIG or F_TRIG function block for counting pulses of CD input signal.
- CTUr, CTDr, CTUDr function blocks operate exactly as other counters, except that all Boolean inputs (CU, CD, RESET, LOAD) have an implicit rising edge A rising edge is the transition of a digital signal from low to high. It is also called positive edge detection included.
FBD Language
FFLD Language
- In the FFLD language, CD is the input rung.
- The output rung is the Q output.
IL Language
(* MyCounter is a declared instance of CTD function block. *)
Op1: CAL MyCounter (CD, LOAD, PV)
FFLD MyCounter.Q
ST Q
FFLD MyCounter.CV
ST CV
ST Language
(* MyCounter is a declared instance of CTD function block. *)
MyCounter (CD, LOAD, PV);
Q := MyCounter.Q;
CV := MyCounter.CV;
See Also
