fanuc-profinet-32bit-real-value-transfer.md

title	FANUC Profinet 32-bit Real Value Transfer Without KAREL
domain	fanuc
subdomain	profinet
tags	profinet real-value 32-bit gi-go plc-communication scara
source	robot-forum.com
status	published
confidence	0.85
created	2026-07-01
verified_date
domain_expert

Problem

SCARA 12iA + R-30iB Compact Plus needs to send/receive 32-bit real values via Profinet, but GI/GO are limited to 16-bit integer groups. KAREL is not available.

Root Cause

FANUC TP register I/O (GI/GO) operates on 16-bit integers only. There are no bitwise operators in TP, and IEEE-754 binary conversion requires bit-level manipulation that TP cannot do natively.

Solution

Use DIV/MOD word-splitting with a scaling factor to pack two 16-bit words into a 32-bit real value.

Sending (Robot → PLC)

R[1:real] = 123.456
R[2:scaled] = ROUND(R[1] * 1000)
R[3:low] = MOD(R[2], 65536)
R[4:high] = (R[2] - R[3]) / 65536
GO[1] = R[3]
GO[2] = R[4]

Receiving (PLC → Robot)

R[3:low] = GI[1]
R[4:high] = GI[2]
R[2:scaled] = R[4] * 65536 + R[3]
R[1:real] = R[2] / 1000.0

Key value: 65536 = 2^16, the 16-bit boundary.

Stopping Robot on DI Signal

Method	Use Case	Notes
HOLD (UOP input)	Pause and resume	Recommended. HOLD=FALSE stops, TRUE resumes
IMSTP	Emergency stop	Immediate, requires restart
Speed 0	Slow stop	Unreliable, Speed+ button overrides

Verification

1. Send a known real value (e.g., 123.456) from robot
2. Verify PLC receives correct high/low words
3. PLC sends back, robot reconstructs: abs(received - original) < 0.001
4. Test with negative values and edge cases near 32767

Notes

• Large integers in registers may overflow — adjust scaling factor if range exceeds ±32.767
• PLC must implement the inverse calculation
• If precision allows, prefer 16-bit direct transfer to simplify architecture
• Source: https://www.robot-forum.com/robotforum/thread/55026/