Ladder — Fanuc Fapt

Mastering Fanuc Fapt Ladder: The Gateway to PMC Diagnostics and Programming

In the world of Computer Numerical Control (CNC) machining, the Fanuc name is ubiquitous. While most operators and programmers are familiar with G-code and the servo side of the control, the logic that governs the machine’s interface—buttons, lights, relays, and safety interlocks—lives in a different world entirely. This is the world of the PMC (Programmable Machine Controller).

For decades, the primary tool used to develop and diagnose this logic was Fanuc Fapt Ladder.

This article explores what Fapt Ladder is, how it functions, and why understanding it remains essential for maintaining legacy CNC machinery. Fanuc Fapt Ladder

1. Built-in PLC Programming on the CNC

• No external PC required: Unlike modern Ladder III software, FAPT Ladder runs directly on the CNC's own CRT/monitor.
• Symbolic programming: Allows the machine builder to write, edit, and document the PLC (PMC) ladder logic using symbols (e.g., "CYCLE_START" instead of just X1.2).

Key points

• Purpose: Create, edit, simulate, and transfer ladder logic to Fanuc controllers (CNCs/robots).
• Compatibility: Works with Fanuc controller families that support ladder programs (verify controller model/version before use).
• Main features: Ladder editor, online/offline simulation, device monitoring, cross-references, program compare, and direct upload/download to controllers.
• Use cases: I/O mapping and diagnostics, sequence control, interlocks/safety logic, retrofitting older machines, and creating operator-facing control logic.
• Benefits: Reduces debugging time, provides clear visual logic, and simplifies controller integration.

A Practical Example

A simple ladder rung for a "Chuck Clamp" might look like this on the Fapt screen:

---[ X1.2 ]---[ X0.5 ]-------------------( Y2.0 )--- Mastering Fanuc Fapt Ladder: The Gateway to PMC

• X1.2 = Foot pedal pressed.
• X0.5 = Chuck is not currently clamped (interlock).
• Y2.0 = Energize the Chuck Clamp Solenoid.

If you see ---[ ]--- (a bracket), it is a normally open contact. If you see ---[\/]---, it is a normally closed contact.

4. Cross-Reference & Search

• Find function: Quickly locate all rungs where a specific address appears.
• Contact/coil cross-reference: Shows if a bit is used as a normally open, normally closed, or coil condition.

The Evolution: From FAPT to Ladder Editor III

To fully understand the "Fanuc Fapt Ladder," you must understand its generational evolution, as this affects how you access it. No external PC required: Unlike modern Ladder III

The Evolution: Fapt Ladder vs. Modern Fanuc Ladder III

It is vital to understand that Fanuc Fapt Ladder is extinct. Modern Fanuc controls (31i, 32i, 0i-D) use Fanuc Ladder III software on a PC. Here is the comparison:

| Feature | Fanuc Fapt Ladder | Fanuc Ladder III (Modern) | | :--- | :--- | :--- | | Interface | Green monochrome CRT, keyboard arrow keys | Windows 10/11 GUI, Mouse driven | | Editor | On-board CNC only | PC software (upload via PCMCIA or Ethernet) | | Search function | Slow, limited to 1 address at a time | Full text search, cross-reference tables | | Backup format | .TF or .FD binary | .LAD or .LPC (convertible to PDF) | | Current status | Obsolete (1995) | Active, supported |

If you are upgrading a machine, you must convert the old Fapt Ladder .FD file to a modern PMC format. This requires a specialized conversion service or an ancient DOS computer running FAPT LADDER-III (DOS version).

Key Features of Fapt Ladder

Fapt Ladder provides a graphical user interface that mirrors the electrical schematics of the machine, making it intuitive for electricians and technicians to read. Its primary features include: