Ready, start, busy, done

Four signals run every robot cell you'll ever integrate: you say start, it says busy, then it says done — and it only listens while it says ready. Learn this loop and you can wire a cell from any brand's manual.

The print

The handshake template is four rungs:

r0  ──[/ES1]───────────────────( RB1.EN )  ∥  ( RB1.P1 )
r1  ──[PB1]──[RB1.RDY]─────────( RB1.START )
r2  ──[RB1.BUSY]───────────────( PL2  IN CYCLE )
r3  ──[RB1.DN]─────────────────( PL1  CYCLE DONE )

Rung 0 enables the robot while the e-stop is released, and parks program 1 on the select bits. Rungs 2 and 3 are just lamps. All the craft is in rung 1.

Why START hides behind READY

RDY is the robot saying two things at once: I'm enabled and I'm idle. Gating the start button through it means the START wire only ever goes high when the robot can actually act on it:

• Mid-cycle? BUSY is high, RDY is low — the button does nothing.
• E-stop in? EN is down, so RDY is down — the button does nothing.

Without that contact, your START wire fires whenever the button feels like it, and now the robot's controller has to decide what a start request during a cycle means. Real controllers log it, alarm on it, or worse — queue it. The RDY contact makes the print say exactly when a start is legitimate.

The edge, the cycle, the memory

Three behaviors to burn in:

• START is an edge. The robot latches the request the instant the signal rises. Hold the button down through the whole cycle and you still get exactly one cycle — at the end, START is still high, so there's no new rising edge. Release and press again: new cycle.
• BUSY is the cycle. High from the start edge to the end of the program — 3.0 s on program 1, longer on the others.
• DN is a memory. It latches at the end of the cycle and stays high until the next start begins. That's why PL1 burns steady between cycles — and why RB1.DN is exactly the contact you'd use to chain what happens after: index the conveyor, open the clamp, count the part.

Run it

Open the handshake circuit and work the panel:

1. Press and release PB1 — watch RDY drop, BUSY carry the cycle with a live countdown, then DONE light and hold.
2. Press PB1 and keep holding it past the end of the cycle. One cycle only — no edge, no restart.
3. Flip the e-stop mid-cycle and watch what happens to everything. Then ask yourself what it takes to come back — that question is module three.