A function calculates a result according to the current value of its inputs. A function has no internal data and is not linked to declared instances. Block - Down counter.
Inputs
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
Q : BOOL TRUE when counter is empty, i.e. when CV = 0
CV : DINT Current value of the counter
Remarks
The counter is empty (CV = 0) when the application starts. The counter does not include a pulse detection for CD input. Use R_TRIG or F_TRIG function block for counting pulses of CD input signal. In FFLD language, CD is the input rung. The output rung is the Q output.
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.
ST Language
(* MyCounter is a declared instance of CTD function block *)
MyCounter (CD, LOAD, PV);
Q := MyCounter.Q;
CV := MyCounter.CV;
FBD Language
FFLD Language
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
See also
