Bit control

1. Why is Bit-Control needed?

In classical control programs behavior arises implicitly:

• Conditions are distributed across the code

• Expectations of signals are not fully described

• Monitoring is performed at points or event-driven

• Diagnosis is created afterwards

This leaves a central question unanswered:

What is allowed, required, or irrelevant – in exactly this state of the machine?

Bit-Control exists to answer this question explicitly, completely and formally to answer.

---

2. What is Bit-Control?

Bit-Control describes the expected and permitted behavior of each zone in every state of a sequence.

It is:

• not program code

• not a safety function

• not a query

• not an event

But:

A formal behavior contract between state and zone.

---

3. Basic principle of Bit-Control

The principle is simple and strict:

• A sequence is in exactly a state

• Each zone has in this state a defined meaning

• This meaning is explicitly defined

Therefore:

No state without evaluation. No zone without meaning.

The result is:

• complete state description

• permanent monitoring

• deterministic behavior

---

4. The Bit-Control matrix

Bit-Control is formally represented as cross table represented:

• Columns → States of the sequence

• Rows → Zones

• Cells → Operands (0, S, i)

This matrix is:

• the model, not the implementation

• complete

• unambiguously

• machine- and human-readable

The Bit-Control matrix describes the entire logical behavior of a sequence.

---

5. The operands

5.1 0 – Don’t Care

Meaning:

• The zone is in this state not relevant

• Nothing is expected

• Nothing is checked

• No reaction occurs

Purpose:

• clear decoupling

• focused models

• avoidance of unnecessary dependencies

---

5.2 S – Sequence Check

Meaning:

• In this state a behavior is expected

• The system:

  • if necessary sets an output

  • waits for a defined feedback

• As soon as the expectation is met:

  • the state is considered fulfilled

  • the transition can take place

Purpose:

• Process control

• operator guidance

• deterministic progression

S describes Progress, not safety.

---

5.3 i – Interlock

Meaning:

• The condition must be met

• In case of deviation:

  • immediate loss of automatic enable

  • stop of the sequence

  • automatic diagnosis

Purpose:

• protection of the process

• prevention of inadmissible state combinations

i protects the logical process, not the machine as a whole.

---

6. Bit-Control and behavior in operation

Bit-Control acts:

• continuously

• dependent on state

• independent of the operating mode

Differences:

• S → leads and waits

• i → monitors and protects

• 0 → consciously ignores

Bit-Control evaluates always the current model state, not events.

---

7. Bit-Control in automatic operation

In automatic operation applies:

• Automatic enable is a prerequisite

• Bit-Control monitors permanently

• When fulfilled S:

  • state is completed

  • transition occurs automatically

• In case of deviation of a i:

  • immediate abort

  • withdrawal of automatic enable

  • diagnosis is generated automatically

It is no additional error logic necessary.

---

8. Bit-Control in manual operation

Also in manual operation applies:

• States remain valid

• Bit control remains active

• Monitoring remains effective

The difference:

• The operator influences zones manually

• The goal is the fulfillment of the current state conditions

A i continues to act as protection:

• no inadmissible movement

• no bypass of the logic

Manual operation is not an exception, but the same logic with a different source of influence.

---

9. Distinction from other monitoring

To clarify:

• Bit-Control ≠ CMZ → CMZ acts independently of state

• Bit-Control ≠ MXIC → MXIC governs manual actions

• Bit-Control ≠ Safety hardware → Bit-Control does not replace an emergency stop chain

Bit-Control protects the process in the model, not physical safety alone.

---

10. Typical mistakes with Bit-Control

Common mistakes are:

• i use it excessively

• S abuse it as a safety replacement

• zones without clear meaning

• states not evaluated completely

• implicit assumptions instead of explicit operands

A good rule of thumb:

If you have to explain why something is the way it is, an operand is missing.

---

11. Why Bit-Control is the core of Selmo

Bit-Control enables:

• complete behavior description

• automatic, correct diagnosis

• clear state logic

• standardizable argumentation

• formal foundation for AI support

Or put differently:

Bit-Control makes machine behavior explainable.

---

12. Summary

Bit-Control is:

• the formal behavior core of Selmo

• explicit, complete and deterministic

• independent of implementation and UI

• Foundation for process, diagnosis and safety

Without Bit-Control there is no verifiable machine model.