If you switch an exclusive keep relay and the machine immediately throws a 1000+ series manufacturer alarm, check the PMC Diagnostic status ( PMC DGN -> STATUS ). Look at the output coils ( Y signals) to see which safety rungs are actively holding the machine back due to an incorrect configuration.
In more complex setups, an entire byte (8 bits) of a keep relay might govern a specific subsystem, such as an automatic tool changer (ATC) or an indexing table. Within that byte, only one specific bit is allowed to be active ( 1 ) at any given time. Activating more than one bit simultaneously creates a logic conflict, resulting in PMC alarms or unexpected machine behavior. Common Applications of Exclusive Keep Relays
Assigned by the MTB for custom machine functions like tool management, coolant control, or interlocks.
In the world of CNC automation, precision control extends far beyond simple G-code programming. Behind every tool change, safety door interlock, and coolant toggle is a complex Programmable Machine Control (PMC) system. For field engineers, maintenance technicians, and system integrators, understanding FANUC keep relays—and specifically how to handle exclusive parameter assignments—is critical for safe and efficient machine operation. fanuc keep relay parameters exclusive
⚠️ : Never use K17, K18, K19, or K900–K927 in your custom ladder logic. Modifying these without deep technical understanding can cause machine malfunctions, display errors, or boot failures.
Unlike D (Data) registers which can be temporary, or R (Internal Relay) bits which are volatile, K parameters are architectural . If one bit is changed, no other feature in the machine should use that same bit for a different purpose.
The exclusive Keep Relay zones provide critical configuration abilities for advanced users and technicians. If you switch an exclusive keep relay and
What or accessory are you trying to toggle?
The screen will display the parameters in a matrix format, showing the byte number (e.g., K0000) and bits 7 through 0.
Before making changes, you must unlock the system parameters. Press the hard key. Press the [SETTING] soft key. Move the cursor to PARAMETER WRITE (PWE) . Within that byte, only one specific bit is
Keep Relays are non-volatile internal relays. They retain their status (0 or 1) even after the CNC machine is powered down. They are represented in the FANUC system as standard bytes, where each byte consists of 8 individual bits (numbered 0 through 7).
Select the or [PMC MNT] soft key, then navigate to [KEEP RELAY] . Search and Edit:
Because Keep Relays are defined by the Machine Tool Builder (like Doosan/DN Solutions, Mori Seiki, or Fanuc Robodrill) rather than FANUC itself, the exact addresses vary. However, the operational logic follows predictable patterns. 1. Clamping Options (ID vs. OD)