sema

 Function Block - Semaphore.

Inputs

Input	Data Type	Range	Unit	Default	Description
CLAIM	BOOL				Takes the semaphore.
RELEASE	BOOL				Releases the semaphore.

Outputs

Output	Data Type	Range	Unit	Description
BUSY	BOOL			TRUE if semaphore is busy.

Remarks

The function block implements this algorithm:

    BUSY := mem;
    if CLAIM then
       mem := TRUE;
    else if RELEASE then
       BUSY := FALSE;
       mem := FALSE;
    end_if;

FBD Language Example

FFLD Language Example

• In the FFLD Language, the input rung is the CLAIM command.
  • The output rung is the BUSY output signal.

IL Language Example

(* MySema is a declared instance of SEMA function block *)
Op1: CAL MySema (CLAIM, RELEASE)
     FFLD  MyBlinker.BUSY
     ST  BUSY

ST Language Example

(* MySema is a declared instance of SEMA function block *)
MySema (CLAIM, RELEASE);
BUSY := MyBlinker.BUSY;