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• CTD / CTD_S

CTD / CTD_S

Type	Function block Available as standard (non-safety-related) and safety-related type (*_S). For the safety-related type, the safety-related data types (SAFE*) are expected at the formal parameters.
Description	Counts down. In case of a rising edge at the input CD and LOAD = FALSE, CV decrements by one. When the value 0 is reached, Q is set to TRUE and the function block stops counting. If LOAD = TRUE, the counter is initialized to the value at PV. To enable counting, the LOAD input must be FALSE. Otherwise the counter will always be re-initialized.
Notes	The inputs CD, LOAD and the output Q can be negated. Note: The negation of formal parameters is not supported in safety-related code (SNOLD). Function blocks have to be instantiated. The instance name of the function block has to be declared in the 'Variables' table of the POU where the FB is going to be used. The instance name must be unique within the POU.
Parameters	Inputs CD Data type: (SAFE)BOOL Description: CV is decreased by one each time the CD input switches from FALSE to TRUE and LOAD=FALSE. LOAD Data type: (SAFE)BOOL Description: If TRUE, the counter is initialized with PV. If FALSE, counting is enabled. As long as LOAD = TRUE, a rising edge from FALSE to TRUE at CD is ignored. LOAD must be FALSE to enable counting, otherwise CV is continually initialized to PV. PV Data type: (SAFE)INT Description: Preset value. Outputs Q Data type: (SAFE)BOOL Description: TRUE if CV = 0. CV Data type: (SAFE)INT Description: Counter result.