CX-PROGRAMMER FUNCTION BLOCK TEACHING EXAMPLE
============================================================
Definition name: FB_PumpFeedback
Body language: Structured Text (ST)
Source basis: Omron W447-E1-18 Function Blocks/Structured Text manual
Purpose: stop-dominant request, permissive, command, feedback timeout,
         retained first-out fault, controlled reset, observable state

IMPORTANT
---------
This is reviewable teaching source, not an importable .CXF library or a
production PLC project. Create the variable table and ST body in the exact
CX-Programmer/CPU/unit-version project, program-check it there, call each
instance with EN continuously ON, and execute the acceptance matrix. The
Tick100ms input must be a one-scan pulse whose timing has been independently
verified. Replace all example timings, addresses, states and safe responses
with approved project values.

VARIABLE TABLE
--------------
Usage,Name,Type,Retain,Description
Input,StartReq,BOOL,No,Start request; edge is detected inside the instance
Input,StopReq,BOOL,No,Stop request; stop dominates start
Input,Permissive,BOOL,No,Combined ordinary-control permissive
Input,RunFb,BOOL,No,Independent running feedback
Input,ResetReq,BOOL,No,Fault reset request; edge is detected inside instance
Input,Tick100ms,BOOL,No,Verified one-scan 100 ms pulse generated outside FB
Input,TimeoutTicks,UINT,No,Feedback timeout in 100 ms ticks; example only
Output,RunCmd,BOOL,No,Ordinary-control run command
Output,Running,BOOL,No,Copy of independently mapped running feedback
Output,Fault,BOOL,Yes,Latched fail-to-start fault
Output,FaultCode,UINT,Yes,0 none; 1 feedback timeout
Output,State,UINT,No,0 idle; 1 commanded; 2 running; 3 fault
Output,ElapsedTicks,UINT,No,Elapsed no-feedback tick count for diagnostics
Internal,RunLatched,BOOL,Yes,Latched run request owned by this instance
Internal,StartMem,BOOL,Yes,Previous StartReq for edge detection
Internal,ResetMem,BOOL,Yes,Previous ResetReq for edge detection
Internal,TickMem,BOOL,Yes,Previous Tick100ms for edge detection
Internal,StartEdge,BOOL,No,One-scan start edge result
Internal,ResetEdge,BOOL,No,One-scan reset edge result
Internal,TickEdge,BOOL,No,One-scan tick edge result

ST BODY
-------
(* Calculate edges before updating their memories. *)
StartEdge := StartReq AND NOT StartMem;
ResetEdge := ResetReq AND NOT ResetMem;
TickEdge := Tick100ms AND NOT TickMem;

StartMem := StartReq;
ResetMem := ResetReq;
TickMem := Tick100ms;

Running := RunFb;

(* Reset is accepted only while command and feedback are both off. *)
IF ResetEdge AND NOT RunCmd AND NOT RunFb THEN
    Fault := FALSE;
    FaultCode := UINT#0;
    ElapsedTicks := UINT#0;
END_IF;

(* Stop and loss of permissive dominate a simultaneous start. *)
IF StopReq OR NOT Permissive THEN
    RunLatched := FALSE;
ELSIF StartEdge AND NOT Fault THEN
    RunLatched := TRUE;
END_IF;

RunCmd := RunLatched AND Permissive AND NOT StopReq AND NOT Fault;

(* Count only verified external tick edges while command lacks feedback. *)
IF RunCmd AND NOT RunFb THEN
    IF TickEdge AND (ElapsedTicks < TimeoutTicks) THEN
        ElapsedTicks := ElapsedTicks + UINT#1;
    END_IF;

    IF (TimeoutTicks > UINT#0) AND (ElapsedTicks >= TimeoutTicks) THEN
        Fault := TRUE;
        FaultCode := UINT#1;
        RunLatched := FALSE;
        RunCmd := FALSE;
    END_IF;
ELSE
    ElapsedTicks := UINT#0;
END_IF;

(* Publish one explicit diagnostic state. *)
IF Fault THEN
    State := UINT#3;
ELSIF RunFb THEN
    State := UINT#2;
ELSIF RunCmd THEN
    State := UINT#1;
ELSE
    State := UINT#0;
END_IF;

CALL-SITE CONTRACT
------------------
1. Create one instance name per independent pump, for example Pump_A_FB.
2. Use the Always ON Flag (P_On) as the EN condition when the edge and
   tick memories must execute continuously. Put process conditions on the
   explicit FB inputs; do not gate the invocation and expect timers/edges
   to initialize while EN is OFF.
3. Map StartReq and ResetReq from bounded request logic, not directly from
   an unreviewed network or HMI address.
4. Map RunFb from an independent validated feedback source.
5. Interlocks and safety functions remain outside this teaching FB under
   their approved ownership. Permissive is ordinary-control context only.
6. Trend StartReq, StopReq, Permissive, RunCmd, RunFb, ElapsedTicks, Fault,
   FaultCode and State during every acceptance test.

EXPECTED 8-SCAN TRACE (TimeoutTicks = 3)
---------------------------------------
Scan,StartReq,StopReq,Permissive,TickEdge,RunFb,RunCmd,ElapsedTicks,Fault,State
1,0,0,1,0,0,0,0,0,0
2,1,0,1,0,0,1,0,0,1
3,0,0,1,1,0,1,1,0,1
4,0,0,1,1,0,1,2,0,1
5,0,0,1,1,0,0,3,1,3
6,0,0,1,0,0,0,0,1,3
7,0,0,1,0,0,0,0,1,3
8,0,0,1,0,0,0,0,0,0  (one ResetReq edge accepted)

The trace assumes each displayed TickEdge is separated by at least one scan
with Tick100ms FALSE. Confirm the actual project trace; do not use this table
as evidence that an untested implementation executed correctly.