HMI Sequence Status Screen: Step Number, Waiting-For Text and Cycle Diagnostics in TIA Portal

• "Waiting for B5 slide bottom" beats "Step 30" – always publish what the step is waiting for.
• Give machine-driven steps a watchdog so a stuck step becomes an alarm, not silence.
• Number steps in tens and keep step names in one text list shared by PLC comments and HMI.

Why a Sequence Status Screen Matters

Most machines run as a step sequence: clamp, drill down, drill up, unclamp, repeat. When such a machine stops without an alarm, it is almost always waiting in a step for a condition that never comes – a sensor that did not switch, a cylinder that did not reach its end, a part that was not loaded. Without a sequence screen, finding that condition means opening the PLC program online. With a good sequence screen, the operator reads it directly: Step 30 DRILL DOWN – Waiting: slide at bottom (B5) – 9.2 / 8.0 s.

What the Sequence Screen Must Show

The screen is a Level 2 display in the HMI display hierarchy, and follows the same grey-when-normal colour rules.

Example: Drilling Station Sequence

A simple drilling station clamps a part, drills it with a vertical slide and releases it. The sequence has seven steps; four of them are driven by the machine and get a watchdog time, three wait for the operator or for home position and have none.

Station I/O

The station follows the same IO mapping rule as the alarm lesson: %I only in FC_InputMapping, %Q only in FC_OutputMapping.

PLC Side: DB_Seq Interface and FB_DrillSeq

Create a global data block DB_Seq as the HMI interface: Step (Int), WaitCode (Int), StepTime_s and StepMax_s (Real), CycleTimeLast_s (Real), CycleCount (DInt), Mode_Auto (Bool), the command bits Cmd_Start, Cmd_StopEOC, Cmd_Reset, Cmd_Next (Bool) and Alarms (Word). Outputs go to DB_SeqOut. Then write the sequence as an SCL function block with a CASE statement:

// FB_DrillSeq – called in OB1 after FC_InputMapping, before FC_OutputMapping
// STAT: Step, StepOld, Wait : Int;  StartReq, StopReq, NextOld, Go : Bool;
//       StepMax : Time;  tStep, tCycle : TON_TIME;

// ---- step timer: restarts on every step change and on RESET
#tStep(IN := (#Step = #StepOld) AND NOT "DB_Seq".Cmd_Reset, PT := T#1H);
#tCycle(IN := #Step >= 20, PT := T#1H);
#StepOld := #Step;

// ---- commands
IF "DB_Seq".Cmd_Reset THEN "DB_Seq".Alarms.%X0 := FALSE; END_IF;
IF "DB_Seq".Cmd_Start THEN #StartReq := TRUE; #StopReq := FALSE; END_IF;
IF "DB_Seq".Cmd_StopEOC THEN #StopReq := TRUE; END_IF;
#Go := ("DB_Seq".Mode_Auto OR ("DB_Seq".Cmd_Next AND NOT #NextOld))
       AND NOT "DB_Seq".Alarms.%X0;              // no transition while timed out
#NextOld := "DB_Seq".Cmd_Next;

// ---- sequence
#Wait := 0;
CASE #Step OF
    0:  // INIT – home position
        IF NOT "DB_IO".B4_SlideTop THEN #Wait := 1;
        ELSIF NOT "DB_IO".B3_ClampOpen THEN #Wait := 2;
        ELSE #Step := 10;
        END_IF;
    10: // READY
        IF #StopReq THEN #StartReq := FALSE; #StopReq := FALSE; END_IF;
        IF NOT #StartReq THEN #Wait := 3;
        ELSIF NOT "DB_IO".B1_PartPresent THEN #Wait := 4;
        ELSIF NOT #Go THEN #Wait := 10;
        ELSE #Step := 20;
        END_IF;
    20: // CLAMP
        IF NOT "DB_IO".B2_ClampClosed THEN #Wait := 5;
        ELSIF NOT #Go THEN #Wait := 10;
        ELSE #Step := 30;
        END_IF;
    30: // DRILL DOWN
        IF NOT "DB_IO".B5_SlideBottom THEN #Wait := 6;
        ELSIF NOT #Go THEN #Wait := 10;
        ELSE #Step := 40;
        END_IF;
    40: // DRILL UP
        IF NOT "DB_IO".B4_SlideTop THEN #Wait := 7;
        ELSIF NOT #Go THEN #Wait := 10;
        ELSE #Step := 50;
        END_IF;
    50: // UNCLAMP
        IF NOT "DB_IO".B3_ClampOpen THEN #Wait := 8;
        ELSIF NOT #Go THEN #Wait := 10;
        ELSE
            "DB_Seq".CycleTimeLast_s := DINT_TO_REAL(TIME_TO_DINT(#tCycle.ET)) / 1000.0;
            "DB_Seq".CycleCount := "DB_Seq".CycleCount + 1;
            #Step := 60;
        END_IF;
    60: // COMPLETE – operator removes the part
        IF "DB_IO".B1_PartPresent THEN #Wait := 9;
        ELSE #Step := 10;
        END_IF;
    ELSE
        #Step := 0;
END_CASE;

// ---- watchdog per step (0 = no watchdog for operator-driven steps)
CASE #Step OF
    20, 50: #StepMax := T#3S;
    30:     #StepMax := T#8S;
    40:     #StepMax := T#6S;
    ELSE    #StepMax := T#0S;
END_CASE;
IF #StepMax > T#0S AND #tStep.ET > #StepMax THEN
    "DB_Seq".Alarms.%X0 := TRUE;                   // HMI discrete alarm: step timeout
END_IF;

// ---- outputs (written to DB_SeqOut, mapped to %Q in FC_OutputMapping)
"DB_SeqOut".Y1_Clamp     := #Step >= 20 AND #Step <= 40;
"DB_SeqOut".Y2_SlideDown := #Step = 30;
"DB_SeqOut".K2_Drill     := (#Step = 30 OR #Step = 40) AND NOT "DB_Seq".Alarms.%X0;

// ---- publish status for the HMI
"DB_Seq".Step       := #Step;
"DB_Seq".WaitCode   := #Wait;
"DB_Seq".StepTime_s := DINT_TO_REAL(TIME_TO_DINT(#tStep.ET)) / 1000.0;
"DB_Seq".StepMax_s  := DINT_TO_REAL(TIME_TO_DINT(#StepMax)) / 1000.0;

• Step timer: IN := Step = StepOld is false for exactly one scan after every step change, so ET always shows time in the current step. RESET also restarts it, so a cleared timeout does not trip again immediately.
• Wait code: each step checks its conditions in order and writes the number of the first missing one. That single integer becomes the waiting-for text on the panel.
• Watchdog: only machine-driven steps have one; operator steps such as loading a part would otherwise raise false alarms.
• STOP at end of cycle: the request is only acted on in step 10, so a part is never left half-drilled.
• Interlocks: in a real machine, add the collective fault from the permissive and interlock logic to #Go and to the outputs.

HMI Side: Tags, Text Lists and the Sequence Screen

Drag DB_Seq into the HMI tag table, then create two text lists: TL_Step with the step names from the step table and TL_Wait with the wait codes below. Add one discrete alarm on DB_Seq_Alarms bit 0 with the text "Drilling station: step timeout" and an output field for the step number in the alarm text.

Header, alarm line and navigation come from the screen template, built exactly as in Build the same HMI screens in TIA Portal. Button behaviour and status lamps are covered in HMI buttons, lamps and auto/manual mode.

Interactive Simulator: Drilling Station Sequence and Status Screen

The station on the left is animated from the same logic as FB_DrillSeq; the panel on the right is the sequence status screen. Load a part, press START and watch the step boxes, the waiting-for text and the step time bar. Then inject a fault and see how the screen tells you exactly where the machine is stuck.

Diagnosing a Stopped Machine with the Sequence Screen

Combine the sequence screen with a trend of cycle time over the shift to see tools wearing or cylinders slowing down; see HMI trends and data logs. For CPU-level diagnosis, use the diagnostic buffer and watch tables.