The robot is just another device

The day the robot shows up on your floor, nobody hands you a robotics degree. They hand you a drawing with a terminal strip on it. Here's the integrator's secret: from the PLC side, the robot is not a program — it's I/O.

A block of points

Add a robot to a panel and you get a block. Wires in, wires out:

The six points on the left are commands — your ladder drives them with ordinary coils:

• EN — the enable. While it's high the robot is allowed to exist as a machine. Drop it and everything stops.
• START — begin the selected program.
• HOLD — pause motion without giving up the cycle.
• RST — clear a fault, once things are safe again.
• P1, P2 — the two program-select bits.

The four bits on the right are status — the robot writes them, your contacts read them: RDY (armed and idle), BUSY (mid-cycle), DN (cycle finished), FLT (something went wrong). And there's one more output that isn't a bit at all: PROG, a word from 0 to 3 — the live echo of the program bits, the kind of value a compare box reads.

You never coil the robot

Notice what's missing: RB1 itself has no bit. You can't put the robot in a rung the way you'd put a motor starter. You coil RB1.EN, you examine RB1.RDY — the device is the collection of its points.

You already know this move. A timer works the same way: nothing ever coils "T1" — a rung drives the TON box, and other rungs read T1.DN. The robot is a timer that costs six figures and moves.

The honest print

This block is a simplified UOP — the User Operator Panel interface that real robots (Fanuc's, most famously) expose for exactly this job. Two things change when you meet the real one:

1. The real safety-side signals are active-LOW. On a real UOP, HOLD and the immediate-stop input are wired so that energized means "allowed to run" — a cut wire or a dead supply reads as STOP. That's fail-safe by construction. Our lab keeps everything active-high so the rungs read naturally; the course will keep reminding you.
2. The real strip is wider — cycle stop, production start, acks, more program bits. The core loop you're about to learn is the same.

See the block live

Open the handshake circuit. Look at the operator panel: the robot has its own card with a live status readout, and every picker in the editor now offers RB1.EN, RB1.RDY and the rest — points, not a device. That's the whole mental model. Next lesson we make it move.