02. I/O Communication

What you'll learn

• 1Distinguish HIWIN's five I/O types and know channel counts·variables
• 2Design a handshake with $DO[n]=TRUE output and WAIT FOR $DI[n]==TRUE
• 3Read the FI/O default mapping (Start/Hold/Stop/Enable, Run/Held/Fault/Ready)
• 4Reproduce the two pick-and-place handshakes (grip·ungrip) as a Python state machine

Introduction

"One wire = one signal." The robot turns $DO on, the partner reads it; the partner turns a response on, the robot reads $DI. This handshake is the core. With no wiring or ports, you practice the logic on one PC.

Key concepts

1) The five I/O types

2) I/O commands and FI/O mapping

Output is `$DO[n]=TRUE/FALSE`; input wait is `WAIT FOR $DI[n]==TRUE` (a blocking command that stops on that line until true). Functional I/O has fixed pin functions: $SI[1]=Start·[2]=Hold·[3]=Stop·[4]=Enable·[5~8]=RSR / $SO[1]=Run·[2]=Held·[3]=Fault·[4]=Ready·[5~8]=ACK.

3) CN6 wiring (NPN)

Digital I/O exits the controller's CN6 port to a terminal block toward the PLC·sensor. Both input and output are NPN (sink) — ON when the signal line is pulled to 0V (GND). Mixing with PNP devices won't work, so match the wiring style.

Core example

Physical I/O can't be created on a PC, so we reproduce the robot↔PLC signal logic as a pure-Python state machine (signals mimicked with a dict).

def handshake(do_pin, do_value, di_pin):
    robot_set_do(do_pin, do_value)   # $DO[n]=TRUE/FALSE
    plc_respond(do_pin, di_pin)      # later, $DI[n]=TRUE response
    robot_wait_for(di_pin)           # WAIT FOR $DI[n]==TRUE

handshake(do_pin=6, do_value=True,  di_pin=1)  # GRIP   → $DI[1] grip done
handshake(do_pin=6, do_value=False, di_pin=4)  # UNGRIP → $DI[4] ungrip done

Common mistakes

Q. WAIT FOR passes immediately instead of waiting.

A. The input is stuck ON (often reversed NPN/PNP wiring). Set CN6 wiring to NPN (sink); in code, reset that $DI bit to False before the next handshake.

Q. I turn $DO on but the partner doesn't react.

A. Wrong output channel/number or no external 24V applied. Recheck the channel number and terminal-block power.

Q. I get an error that $RI/$RO or $SI/$SO doesn't exist.

A. RI/O isn't supported on SCARA·Delta — use DI/O·MI/O. SI/O needs a Fieldbus option card installed.

Summary

• Learned the five I/O types' variables·channels·commands
• $DO output → partner response → WAIT FOR $DI handshake is the base pattern of all automation
• FI/O has fixed pin functions (Start/Hold/Stop/Enable, Run/Held/Fault/Ready)
• From the Modbus lessons on, these signals are exchanged as coil/register bits in software

Exercises

1. Run the pick-and-place cycle and confirm GRIP/UNGRIP handshakes run in order
2. Remove the $DI reset to reproduce WAIT FOR passing immediately, and explain why
3. From the FI/O table, write down the pin numbers for Start/Enable/Ready