Fanuc keep relay parameters, denoted by the K address, are non-volatile memory bits used within the Programmable Machine Controller (PMC) to manage machine-specific logic and system configurations. Unlike standard internal relays (R) that reset when power is lost, keep relays retain their state (0 or 1) even after a machine shutdown, making them essential for persistent settings like tool change flags, interlocks, and optional hardware toggles. Core Functions of Keep Relay Parameters

The primary "exclusive" role of keep relays is to act as software-driven switches that bridge the gap between fixed CNC parameters and the machine tool builder's (MTB) custom ladder logic.

Function Toggling: Builders use keep relays to "use or not use" specific machine units, such as enabling/disabling a chip conveyor, high-pressure coolant, or an automatic door. System Configuration: Certain keep relays (specifically

) are reserved for Fanuc system functions, such as enabling ladder editing or controlling how data is backed up to flash memory.

Maintenance & Debugging: For troubleshooting, keep relays can be used to bypass physical sensor alarms or simulate signals (like a "work gap sensor") during machine setup. Address Structure and Bit Significance

Keep relays are organized by address (e.g., K0, K1, K2) and then by individual bits (0 through 7).

K00–K15: Typically reserved for builder-defined machine sequence logic.

K17–K19: Exclusively used for PMC management software data and should not be used for custom machine sequences unless specified by Fanuc.

K900 and above: Often designated as "System Keep Relays" that handle internal CNC-to-PMC communication states. How to Modify Keep Relay Parameters

Changing these parameters requires cautious access to the PMC maintenance screens. Enable Parameter Write (PWE): Set the machine to MDI mode.

Press the [OFFSET/SETTING] key, find the "SETTING" soft key, and change "PARAMETER WRITE" from 0 to 1. Navigate to PMC Maintenance: Press the [SYSTEM] function key.

Select the [PMC] or [PMC MNT] soft key, then navigate to [KEEP RELAY]. Search and Edit:

Key in the desired K-address (e.g., K17) and press [SEARCH].

Move the cursor to the specific bit and enter the new value (0 or 1). Security Measures:

After changes, return the PARAMETER WRITE setting to 0 to prevent accidental modifications. Common Exclusive Use Examples Get to know how to change the Keep Relay!

Fanuc Keep Relay Parameters Exclusive: A Comprehensive Guide

In the world of industrial automation, Fanuc is a well-known and respected brand that provides a wide range of products and solutions for various industries. One of the key aspects of Fanuc's control systems is the use of relay parameters, which play a crucial role in ensuring the smooth operation of machinery and equipment. In this article, we will explore the concept of Fanuc keep relay parameters exclusive, its importance, and how to configure and maintain these parameters.

What are Relay Parameters?

Relay parameters are a set of values that are used to configure and control the behavior of relays in a Fanuc control system. Relays are electrical devices that are used to switch circuits on and off, and they are commonly used in industrial automation applications to control various types of equipment, such as motors, pumps, and valves. In a Fanuc control system, relay parameters are used to define the characteristics of the relays, such as their timing, logic, and output behavior.

What are Fanuc Keep Relay Parameters Exclusive?

Fanuc keep relay parameters exclusive refers to the ability to maintain the relay parameters in a Fanuc control system, even when the power is turned off or the system is restarted. This means that the relay parameters are retained in memory, allowing the system to resume operation with the same settings as before. This feature is essential in many industrial automation applications, where the settings of the relays need to be maintained consistently over time.

Why are Fanuc Keep Relay Parameters Exclusive Important?

The importance of Fanuc keep relay parameters exclusive cannot be overstated. Here are some reasons why:

  1. Consistency: By maintaining the relay parameters, you can ensure that the system operates consistently, even after a power failure or restart. This is critical in many industrial automation applications, where consistency is essential for product quality, safety, and efficiency.
  2. Reduced Downtime: If the relay parameters are lost, it can take a significant amount of time to reconfigure the system, which can lead to downtime and lost productivity. By maintaining the relay parameters, you can minimize downtime and ensure that the system is up and running quickly.
  3. Increased Safety: In some applications, the settings of the relays are critical for safety reasons. For example, in a safety-critical system, the relay parameters may need to be set to ensure that the system responds correctly in an emergency situation. By maintaining the relay parameters, you can ensure that the system operates safely, even after a power failure or restart.

How to Configure Fanuc Keep Relay Parameters Exclusive

Configuring Fanuc keep relay parameters exclusive is a straightforward process that can be done using the Fanuc control system's programming software. Here are the general steps:

  1. Access the Programming Software: The first step is to access the programming software for the Fanuc control system. This software is typically provided by Fanuc and can be used to configure and program the system.
  2. Navigate to the Relay Parameters Menu: Once you have accessed the programming software, navigate to the relay parameters menu. This menu will typically be labeled as "Relay Parameters" or "Keep Relay Parameters".
  3. Select the Relay Parameters to be Maintained: In the relay parameters menu, select the relay parameters that you want to maintain. These may include parameters such as timing, logic, and output behavior.
  4. Set the Keep Relay Parameters Option: Once you have selected the relay parameters, set the "Keep Relay Parameters" option to "Yes" or "Enabled". This will ensure that the relay parameters are maintained in memory, even when the power is turned off or the system is restarted.

Best Practices for Maintaining Fanuc Keep Relay Parameters Exclusive

Here are some best practices for maintaining Fanuc keep relay parameters exclusive:

  1. Regularly Backup the System: Regularly backup the Fanuc control system to ensure that the relay parameters are safe in case of a system failure.
  2. Use a Battery-Backed Memory: Use a battery-backed memory to ensure that the relay parameters are maintained, even in the event of a power failure.
  3. Test the System Regularly: Test the Fanuc control system regularly to ensure that the relay parameters are being maintained correctly.
  4. Document the Relay Parameters: Document the relay parameters and their settings to ensure that they can be easily reconfigured in case of a system failure.

Common Issues with Fanuc Keep Relay Parameters Exclusive

Here are some common issues that may occur with Fanuc keep relay parameters exclusive:

  1. Loss of Relay Parameters: If the relay parameters are lost, it can cause the system to malfunction or operate incorrectly.
  2. Incorrect Configuration: If the relay parameters are not configured correctly, it can cause the system to operate incorrectly or safely.
  3. Memory Failure: If the memory fails, it can cause the relay parameters to be lost, which can lead to system downtime.

Troubleshooting Fanuc Keep Relay Parameters Exclusive

If you are experiencing issues with Fanuc keep relay parameters exclusive, here are some troubleshooting steps:

  1. Check the System Configuration: Check the system configuration to ensure that the relay parameters are set correctly.
  2. Check the Memory: Check the memory to ensure that it is functioning correctly and that the relay parameters are being maintained.
  3. Check the Backup: Check the backup system to ensure that it is functioning correctly and that the relay parameters are being backed up.

Conclusion

In conclusion, Fanuc keep relay parameters exclusive is a critical feature that ensures the smooth operation of machinery and equipment in industrial automation applications. By maintaining the relay parameters, you can ensure consistency, reduce downtime, and increase safety. By following the best practices outlined in this article, you can ensure that the relay parameters are maintained correctly and that the system operates safely and efficiently. If you are experiencing issues with Fanuc keep relay parameters exclusive, the troubleshooting steps outlined in this article can help you to resolve the issue quickly and efficiently.

The hum of the shop floor was a constant companion for Elias, a veteran maintenance tech. Today, the challenge was a new CNC lathe that refused to engage its bar feeder and parts catcher simultaneously. It was a classic "either-or" scenario, and Elias knew the secret lay within the Fanuc Keep Relays. The Logic of the Keep Relay In the world of Fanuc CNCs, Keep Relays (

parameters) act as the machine’s long-term memory for logic toggles. Unlike volatile signals, these stay set even after the power is cycled. Elias opened the PMCLAD (Programmable Machine Control) screen and found the culprits: K0001.0cap K 0001.0 for the bar feeder and K0001.1cap K 0001.1 for the parts catcher. The Problem: Mutual Exclusivity

The machine builder had programmed these two functions to be mutually exclusive. In the ladder logic, a "Safety Interlock" was written so that if one bit was (ON), the other was forced to (OFF).

The Conflict: The bar feeder required the machine to know it had "material ready," while the parts catcher needed to know the "door was clear." The Overlap: If Elias turned on K0001.0cap K 0001.0 , the ladder logic would automatically "coil off" K0001.1cap K 0001.1 to prevent a mechanical crash. Resolving the Lock

Elias realized he wasn't just fighting a setting; he was navigating the Machine Builder's (OEM) Safety Logic. To make them work together safely, he had to:

Enable Parameter Write: He navigated to the Setting Screen and flipped Parameter Write Enable (PWE) to .

Monitor the PMC: He watched the ladder in real-time. He saw that the "Exclusive" nature was a software "handshake." Adjust the Keep Relay: By toggling a different relay, K012.4cap K 012.4

(the "Integrated Mode" bit defined in the manufacturer's manual), he bridged the two functions.

The machine finally clicked. The bar feeder pushed, the parts catcher waited its turn, and the exclusivity was resolved without a single alarm. Elias turned PWE back to

, cleared the "100 ALARM" (Parameter Write Enable), and watched the first perfect part drop into the bin.

Review: FANUC Keep Relay Parameters Exclusive

Introduction

FANUC, a renowned leader in the field of industrial automation and CNC systems, has been continuously innovating to provide robust and efficient solutions for manufacturing processes. One of its significant features in certain models is the ability to keep relay parameters exclusive. This review aims to delve into the specifics of this feature, its implications, benefits, and potential drawbacks.

Understanding Keep Relay Parameters Exclusive

In FANUC's CNC systems, parameters are crucial as they define the operational characteristics of the machine. The "keep relay parameters exclusive" feature refers to a setting or function that allows certain parameters related to relay outputs to be preserved or kept unique, even during power cycles or system resets. This ensures that specific configurations or settings for relay outputs are maintained, providing consistency and reliability in the machine's operation.

Benefits

  1. Consistency and Reliability: By keeping relay parameters exclusive, machines can operate consistently, as critical settings are preserved. This is particularly important in manufacturing environments where consistency is key to product quality.

  2. Reduced Downtime: Since specific settings are retained, there's less need for reconfiguration after power outages or system resets, thereby reducing downtime and increasing overall productivity.

  3. Enhanced Control: This feature provides operators with enhanced control over the machine's outputs, allowing for customized operation that meets specific needs or safety requirements.

  4. Simplified Troubleshooting: With known settings consistently applied, troubleshooting becomes more straightforward, as the system's behavior is more predictable.

Potential Drawbacks

  1. Complexity: For users not familiar with FANUC systems or CNC parameter settings, managing exclusive relay parameters can add a layer of complexity to machine operation and maintenance.

  2. Security and Access Control: If not properly secured, the ability to change these parameters could lead to unauthorized alterations, potentially disrupting operations.

Conclusion

The "keep relay parameters exclusive" feature in FANUC's CNC systems represents a valuable tool for ensuring operational consistency, reducing downtime, and enhancing control over machine outputs. While it presents a few challenges, particularly in terms of complexity and security, the benefits it offers make it a significant advantage for industries relying on precise and reliable machinery operations. As FANUC continues to evolve its technologies, features like these will likely play a crucial role in advancing industrial automation.

Rating: 4.5/5

This rating reflects the feature's substantial benefits and its potential to improve operational efficiency, with a slight deduction for the complexity and potential security concerns it may introduce. Overall, it's a powerful feature that, when properly managed, can significantly enhance the performance and reliability of FANUC CNC systems.

In Fanuc CNC systems, Keep Relays (K-parameters) are software-based latching relays within the Programmable Machine Control (PMC) that maintain their state (ON or OFF) even after the power is cycled. These parameters are primarily used by machine tool builders to enable or disable specific machine options, bypass sensors for maintenance, or configure custom logic without rewriting the entire ladder program. Key Characteristics of Keep Relays

Non-Volatile Memory: Values are stored in non-volatile memory, ensuring that settings like a chip conveyor's "on" status or safety bypasses persist after a restart.

Address Structure: Addresses are typically represented in an 8-bit format (e.g., K0.0 to K0.7). Some ranges are reserved for system functions (often K900+), while others are for machine-specific OEM functions.

Maintenance & Debugging: They are vital for bypassing faulty sensors (like a conveyor rotation sensor) to keep production running while awaiting repairs. Accessing and Modifying Keep Relays

To modify these parameters, you generally need to put the machine in MDI mode and enable "Parameter Write".

Enable Parameter Write: Navigate to the Setting Screen and set PARAMETER WRITE to 1. Navigate to PMC Maintenance: Press the SYSTEM key. Select the PMC soft key. Choose PMCPRM (PMC Parameters) and then KEEP-RL.

Safety Precautions: For certain system keep relays (like K900), values may only be visible or changeable when the Emergency Stop is pressed. Common Applications

Machine Options: Enabling/disabling features like chip conveyors, coolant types, or tool management systems.

Logic Interlocks: Modifying turret rotation requirements (e.g., allowing rotation without requiring the X/Y axes to be at home) to reduce cycle time.

System Controls: Bypassing safety circuit interfaces or hiding specific system screens. Important Documentation

Because keep relay assignments are determined by the Machine Tool Builder (MTB), their functions vary between machines. It is critical to consult the machine’s Ladder Diagram or Maintenance Manual provided by the manufacturer to identify what each specific K-address controls. Fanuc Keep Relay Parameters Overview | PDF - Scribd

In Fanuc CNC systems, Keep Relays (K-parameters) are specific memory addresses that store binary (0 or 1) settings to control machine behavior or enable/disable PLC functions. Unlike standard NC parameters, Keep Relays are often defined by the Machine Tool Builder (MTB)

, meaning their functions are exclusive to the specific machine model or manufacturer. 1. Understanding Exclusive Functions

Because Keep Relays are PLC-based (PMC), they are used to manage functions that are not built directly into the Fanuc software but are instead added by the builder. Customization:

Builders use K-relays to toggle features like tool changers, door interlocks, or coolant options. Non-Volatile:

They are "kept" in memory even when power is turned off, ensuring the machine configuration remains stable. Variable Use:

K0 through K15 are typically reserved for the machine sequence (builder-defined), while K16 and higher are often reserved for system management. 2. Common Keep Relay Examples

While functions vary, many builders follow similar patterns for common machine operations: Typical Function Description Reference Return May force a homing sequence before automatic operation. Door Interlock Enables or bypasses safety door lock signals. ATC Configuration

Selects between different tool changer types (e.g., Rack vs. Umbrella). Spindle Safety

Controls if the spindle can rotate while the door is unlocked. System Access

Often used to enable specialized menus for loading/saving ladder diagrams. 3. How to Modify Keep Relays

To change an exclusive K-relay setting, you must typically follow these steps to unlock the system: Enable PWE: , press the OFFSET/SETTING key, find the "SETTING" soft key, and change PARAMETER WRITE (PWE) from 0 to 1. Navigate to PMC: hard key, then use the right arrow soft keys to find PMC MAINTENANCE Access Keep Relays: Select the KEEP RELAY Edit Values:

Use the cursor to find the target address (e.g., K5.4). Note that bits are read right to left (Bit 0 to Bit 7). Save & Reset:

Change the bit to 1 or 0, then immediately return to the Setting screen to set PWE back to 0 4. Critical Documentation

Because Keep Relay assignments are unique to each builder, you should always consult the following: Machine Builder's Ladder Diagram: Often found in the back of the electrical manual. Maintenance Manual:

Look for the "PMC Parameter List" section specific to your machine's serial number. Ladder Search:

If documentation is missing, you can search for the "K" address directly within the PLC ladder on the CNC screen to see what output it triggers. Fryer Machine Systems How to Enable Parameter Write Enable (PWE) on a Fanuc CNC

Fanuc Keep Relays (K-parameters) are non-volatile PMC (Programmable Machine Control) parameters used to toggle machine-specific functions. Unlike standard NC parameters that control motion, keep relays act as software "switches" that remain in their state (0 or 1) even after power is turned off. Core Functionality

Keep relays are used by machine tool builders (MTBs) to define machine behavior without rewriting the PLC ladder. They are typically used for:

Feature Selection: Enabling or disabling options like a chip conveyor, high-pressure coolant, or an optional tool magazine.

Interlock Control: Bypassing or enforcing safety interlocks, such as door locks or spindle start conditions.

Operational Modes: Switching between different tool change (ATC) patterns or pallet change (APC) sequences. Common Keep Relay Addresses

While addresses vary by machine builder, standard Fanuc-defined ranges often include: K0 – K15: General bit parameters for machine sequences. K16: Often used for keep-type memory control.

K17 – K19: Reserved for PMC managing software data; these should generally not be used for custom sequences.

K900+: High-range addresses often reserved for internal Fanuc system functions. How to Access and Modify Keep Relays

Modifying these parameters requires entering "Parameter Write Enable" (PWE) mode first. Enable Parameter Write: Press the MDI button on the control. Press the OFFSET/SETTING function key.

Navigate to the "Setting" page and change PARAMETER WRITE from 0 to 1. Navigate to PMC Maintenance: Press the SYSTEM function key. Press the [PMC] soft key, then [PMCPRM] or [PMC PARAM]. Press the [KEEPRL] or [KEEP RELAY] soft key. Edit the Parameter:

Use the cursor keys to find the specific K-address (e.g., K0005). Bits are numbered 7 6 5 4 3 2 1 0 from left to right. Type the new bit value (0 or 1) and press INPUT. Reset Safety:

Return to the OFFSET/SETTING screen and set PARAMETER WRITE back to 0. Machine-Specific Examples

Turret Rotation (K17.5): On some turning centers, changing this can allow the turret to rotate without returning to home position, reducing cycle times.

Chuck Clamp (K7.6): Can be used to toggle whether the machine checks for a clamp signal before starting the spindle.

Internal Programmer (K17.1): Toggling this bit may allow or prevent on-machine editing of the PMC ladder.

Warning: Keep relay definitions are unique to your machine's MTB. Always refer to the Fanuc Maintenance Manual or the machine-specific electrical manual before making changes to avoid unintended mechanical movements. Fanuc Keep Relay Parameters Overview | PDF - Scribd

How to Override Exclusivity (Legitimate Methods Only)

If you have lost the password or the OEM is out of business, here are the legal ways to gain exclusive access to Keep Relays:

  1. Full Memory Clear (The Nuclear Option): Clearing all CNC memory (Service Menu → Clear SRAM) will reset Keep Relays to the ladder’s default state. This erases all programs, offsets, and parameters. Only do this if you have a complete backup.
  2. PMC Ladder Reload: Reloading the original .LAD file from the builder (via Memory Card) overwrites all Keep Relays to their exclusive factory defaults.
  3. Factory Password Request: Contact the builder with your machine serial number. They often provide a one-time password to unlock exclusive K parameter ranges.

Never download third-party cracking tools. Illegal modification of safety-related Keep Relays is a violation of OSHA/ISO machinery safety standards.

Best Practices for Maintaining Exclusivity

1. Machine Builder Exclusive (OEM Privilege)

Fanuc provides the hardware and core firmware, but the Machine Tool Builder (e.g., Haas, Mazak, DMG MORI, Doosan) defines the Keep Relay map. This means:

  • K1.0 might mean "Chip Conveyor Enabled" on a Mori lathe, but "Safety Door Lock Override" on a Doosan mill.
  • The function of each Keep Relay is exclusive to that specific builder’s ladder logic.
  • There is no universal cross-reference. You cannot assume K10.3 on one machine does the same thing on another.

Best Practices

  • Do not use listed exclusive K relays in user ladder logic for other purposes.
  • Document any exclusive K relays modified during commissioning.
  • Lock exclusive K relays in the PMC parameter protection menu where available.
  • Consult FANUC before modifying a K relay whose function is not explicitly explained in OEM documentation.

Note: Exact exclusive Keep Relay addresses vary by FANUC controller series and PMC model (Ladder I, II, III, etc.). Always verify against the specific controller’s manual set.

Title: The Guardians of Automation: The Criticality and Application of FANUC Keep Relay Parameters

In the intricate ecosystem of FANUC CNC systems, the distinction between volatile memory and non-volatile memory is the line between a machine that remembers its purpose and one that resets to oblivion upon reboot. At the heart of this distinction lies the "Keep Relay" (often designated by addresses beginning with the letter 'K'). While standard Relays (R, D, or E addresses) are essential for the logical flow of a program, Keep Relay parameters occupy an exclusive and critical tier within the ladder logic architecture. They serve as the system’s long-term memory, preserving vital operational states and configuration settings even when power is removed. Understanding the exclusive nature of Keep Relay parameters is essential for any engineer or technician aiming to maintain system integrity and prevent catastrophic data loss.

The primary defining characteristic of a Keep Relay is its non-volatility. In standard relay logic, when the power supply to the CNC unit is turned off, all relay coils are de-energized, and their contacts revert to their default states. This is acceptable for transient signals—such as a command to open a chuck or start a spindle—but it is unacceptable for data that defines the machine’s personality. Keep Relays solve this by storing their status (ON or OFF) in non-volatile memory backed by a battery or solid-state memory retention. This exclusivity means that if a Keep Relay is set to '1' (ON), it will remain '1' even after the machine is shut down, shipped across the country, and restarted. This unique property makes them indispensable for storing "latched" states, such as whether a maintenance interval has been reached, whether a specific optional function is enabled, or the last position of a tool changer.

Furthermore, the exclusivity of Keep Relay parameters extends to their role in system configuration and customization. Unlike standard internal relays, which are purely for the programmer’s logical processing, Keep Relays often bridge the gap between the PMC (Programmable Machine Controller) and the CNC system parameters. In many FANUC architectures, specific Keep Relays are hard-coded or reserved for system-level functions. For example, a specific bit in a Keep Relay might be used to enable a custom macro interface or activate a specific safety interlock that must remain active regardless of power cycles. In custom machine building, these relays are frequently used to create "personality bits"—settings that allow a single generic ladder program to adapt to different machine variants (e.g., a lathe versus a mill) by simply flipping a Keep Relay switch.

However, the power of Keep Relays comes with a significant engineering responsibility: the risk of "latched" logic errors. Because these relays retain their state, they do not naturally reset to a "safe" default state upon power-up like standard relays do. If a Keep Relay is used to latch an error state or an unsafe condition, simply cycling power will not clear the fault; the machine will wake up in an error state. Therefore, the logic surrounding Keep Relays must be exclusive and rigorous. It usually requires an explicit "unlatch" or reset condition in the ladder logic. If a technician mistakenly uses a Keep Relay for a transient signal (like a pulse to trigger a single cycle), the machine may get stuck in that cycle indefinitely. This highlights the necessity for programmers to treat Keep Relays not as general-purpose variables, but as permanent registers reserved for specific, persistent data.

The maintenance of Keep Relay parameters also requires a specialized approach compared to standard logic. In the event of a battery failure or a full memory clear, the states of these relays are lost, potentially rendering the machine inoperable until the correct "bit patterns" are restored. This underscores the importance of documentation and backup. A skilled technician knows that a backup of the PMC SRAM (Static Random Access Memory) is useless without a record of the Keep Relay states. Consequently, many facilities maintain a "Parameter Sheet" exclusively listing the active Keep Relays and their intended functions, treating them with the same reverence as the servo tuning parameters.

In conclusion, Keep Relay parameters

Best Practices for Managing Exclusive Keep Relays

Whether you are a machine rebuilder or an in-house maintenance lead, follow these protocols:

| Practice | Why It Matters | | :--- | :--- | | Backup ALL Keep Relays | Use Fanuc’s I/O screen to output the PMC parameters (including Keep Relays) to a memory card. | | Document Every Change | Create a log: Date, Address (e.g., K0012.3), Old Value, New Value, Reason. | | Never Trust Defaults | If you reload generic Fanuc parameters from a donor machine, you will overwrite the exclusive Keep Relays with the wrong ones. Always use the machine-specific backup. | | Know Your Access Level | Operator = View only. Maintenance = Change non-exclusive K values. OEM = Change exclusive locked K values via password. | | Use the PMC Ladder Search | To find what a Keep Relay does, go to PMCLAD, press SEARCH, enter the K address (e.g., K5.2). The ladder will highlight exactly where that bit is used. |

Conclusion

The Fanuc Keep Relay parameter is exclusive not by accident but by architectural design. It is functionally exclusive, speaking only to the ladder logic, not to G-code. It is access exclusive, hidden behind service menus and passwords. It is application exclusive, giving each machine builder the power to define binary behaviors that standard parameters cannot. And it is strategically exclusive, serving as both a diagnostic tool and a security gate.

In the broader ecosystem of CNC parameters, where axis gains and feed-forward coefficients often steal the spotlight, the humble Keep Relay remains the quiet, exclusive gatekeeper of machine logic. Understanding its unique role is the mark of a true controls professional—one who recognizes that sometimes the smallest bits of memory carry the most significant authority over a machine’s soul.

❌ Don’ts:

  • Don’t assume a bit is free just because it’s not mentioned in the operator’s manual. Many custom ladder functions use undocumented K bits.
  • Don’t change a K parameter while the machine is in auto cycle unless the builder explicitly states it’s safe. Some ladder logic reads K bits only at power-up.
  • Don’t share the same K bit for complementary functions unless using a “mask” (multiple bits combined).