SF_CTUD (FB)

Description of the function block

Tip

The version of the function block as described here corresponds to the latest version of the function block in Version list of function blocks.

Tip

SF_CTUD is a counter FB from the SafetyStandard library. It is an extension of CTUD, a standard IEC 61131-3 function block. The SF_CTUD function block contains both standard data types and safety-related data types (prefix: SAFE).

SF_CTUD fulfills the function of an up and down counter.

Figure 112. Function block: SF_CTUD

Table 89. VAR_INPUT

Name	Data Type	Initial Value	Description, parameter values
`CU`	`BOOL`	`FALSE`	Rising edge at `CU` increments `CV` by `1`.
`CD`	`BOOL`	`FALSE`	Rising edge at `CD` decrements `CV` by `1`.
`RESET`	`BOOL`	`FALSE`	`TRUE`: Resets the `CV` counter to `0`. `FALSE`: Counting up is enabled.
`LOAD`	`BOOL`	`FALSE`	`TRUE`: Sets `CV` to the initial value `PV` `FALSE`: Counting down is enabled.
`PV`	`SAFEINT`	`0`	Start value (count down) /or upper limit for incrementing `CV`

Table 90. VAR_OUTPUT

Name	Data Type	Initial Value	Description, parameter values
`QU`	`SAFEBOOL`	`FALSE`	`TRUE`: Counter `CV` has reached the upper limit.
`QD`	`SAFEBOOL`	`FALSE`	`TRUE` : Counter `CV` has reached 0.
`CV`	`SAFEINT`	`0`	Current counter value of the counter `CV`.

FB code

IF R THEN CV := 0 ;
ESLIF LOAD THEN CV := PV ;
ELSE
            IF NOT (CU AND CD) THEN
                            IF CU AND (CV < PVmax)
                            THEN CV := CV+1;
                            ELSIF CD AND (CV > PVmin)
                            THEN CV := CV-1;
                            END_IF;
            ENDIF;
ENDIF;
QU := (CV >= PV) ;
QD := (CV <= 0);

The numerical value of PVmin is 0. The numerical value of PVmax is 32767.