A function block groups an algorithm and a set of private data. It has inputs and outputs. - Semaphore.
Inputs
CLAIM :
BOOL Takes the semaphore
RELEASE : BOOL
Releases the semaphore
Outputs
BUSY : BOOL True if semaphore is busy
Remarks
The function block implements the following algorithm:
BUSY := mem;
if CLAIM then
mem := TRUE;
else if RELEASE then
BUSY := FALSE;
mem := FALSE;
end_if;
In FFLD language, the input rung is the CLAIM command. The output rung is the BUSY output signal.
ST Language
(* MySema is a declared instance of SEMA function block *)
MySema (CLAIM, RELEASE);
BUSY := MyBlinker.BUSY;
FBD Language
FFLD Language
IL Language:
(* MySema is a declared instance of SEMA function block *)
Op1: CAL MySema (CLAIM, RELEASE)
FFLD MyBlinker.BUSY
ST BUSY
