CTUD / CTUD_S - Counter Up/Down

This counter function block counts up or down. In case of a rising edge at the input CU, CV is increased by one. In case of a rising edge at the input CD, CV decrements by one. If CV = PV, QU is set to TRUE. If CV = 0, QD is set to TRUE. If RESET = TRUE, the counter is initialized with 0. If LOAD = TRUE, the counter is initialized with PV. To enable the counting process, the inputs RESET and LOAD must be FALSE. Otherwise the counter will always be re-initialized.

The function block is available as standard function block CTUD and safety-related function block CTUD_S.

CTUD

Parameter	Data types	Description
CU	BOOL	If a rising edge is detected, CV is increased by one.
CD	BOOL	If a rising edge is detected, CV decrements by one.
RESET	BOOL	If TRUE, the counter is initialized with 0. If FALSE, counting is enabled.
LOAD	BOOL	If TRUE, the counter is initialized with PV. If FALSE, counting is enabled.
PV	INT	Preset value
QU	BOOL	TRUE if CV = PV
QD	BOOL	TRUE if CV = 0
CV	INT	Counter result

CTUD_S

Parameter	Data types	Description
CU	SAFEBOOL	If a rising edge is detected, CV is increased by one.
CD	SAFEBOOL	If a rising edge is detected, CV decrements by one.
RESET	SAFEBOOL	If TRUE, the counter is initialized with 0. If FALSE, counting is enabled.
LOAD	SAFEBOOL	If TRUE, the counter is initialized with PV. If FALSE, counting is enabled.
PV	SAFEINT	Preset value
QU	SAFEBOOL	TRUE if CV = PV
QD	SAFEBOOL	TRUE if CV = 0
CV	SAFEINT	Counter result

NOTE:

Function blocks have to be instantiated. Like variables, instances have to be declared before they can be inserted in a code body. Instances must be unique within the POU. In the following example, the instance name 'CTUD_S_1' is used.

Example for a safety-related function block declaration CTUD_S

Variables declarations

Local declarations:

Global declarations (I/O variables):

NOTE:

If you want to use the standard function block CTUD in your code worksheet, you have to select the data type 'CTUD' for the function block instance in the local variables worksheet. Accordingly, the data types 'BOOL' and 'INT' must be used instead of 'SAFEBOOL' and 'SAFEINT'.