APHELION

FieldReg · Modbus decoder · iOS

Every byte order, decoded at once.

FieldReg is an offline Modbus / PLC register toolkit for the iPhone in your pocket. Decode 1, 2, or 4 registers into every interpretation at the same time — signed and unsigned integers, FLOAT32/64, in all four byte orders — plus address conversion, 4–20 mA loop maths, a bit & CRC inspector, and eight offline field sheets. It never phones home.

100% offline No account Data not collected One-time unlock

Download on the App Store

FieldReg Decode screen: two 16-bit registers decoded into UINT32 across big-endian, word-swapped and other byte orders simultaneously.
Decode
FieldReg Address screen: holding register 40001 shown as protocol 0-based, 1-based data model, 5-digit and 6-digit references with read/write function codes.
Address
FieldReg Scale screen: a 4–20 mA loop preset over a 0–500 m³/h range, with a loop calculator converting 12 mA to 50 percent.
Scale · 4–20 mA
FieldReg Bits & CRC screen: a tappable 16-bit word inspector for 0xA55A with live hex, unsigned, signed, binary and octal bases.
Bits & CRC
FieldReg Reference screen: a searchable library of offline field sheets including function codes, exception codes, frame anatomy and RS-485 wiring.
Reference
FieldReg RS-485 field-wiring reference sheet covering topology, 2-wire versus 4-wire, the A/B naming chaos, termination, bias and grounding.
RS-485 sheet

Scroll · six screens, all working in airplane mode

Five tools, plus a promise

Built by a controls engineer, for the people in front of the panel.

No connection, no account, no clutter — just the maths you reach for at the panel, every interpretation on screen at once.

Decode

Every interpretation

1, 2, or 4 registers as signed/unsigned ints and FLOAT32/64 across ABCD, CDAB, BADC and DCBA — with a plausibility flag pointing at the value that makes physical sense. Hex or decimal entry, smart paste, one-tap word swap, automatic history.

Address

Every notation

Protocol 0-based ↔ 1-based data model ↔ 40001 ↔ 400001, with the read and write function codes for each entity. Enter any reference and the entity follows.

Scale

Loop maths, instantly

Linear scaling and a 4–20 mA loop calculator with NAMUR range flags. 0/25/50/75/100% injection tables you can export as CSV straight into the loop-check record. Save instrument presets.

Bits & CRC

Down to the bit

A tappable 16-bit grid with hex, decimal, binary and octal live side by side, and CRC-16/MODBUS with the on-wire byte order spelled out.

Reference

Eight field sheets

Function codes, exception codes, RTU/TCP framing, RS-485 wiring, serial gotchas, data types & byte orders, PLC addressing, and the 4–20 mA quick sheet — all offline.

Private

Never phones home

No accounts, no analytics, no tracking. Your register values never leave the device — the App Store privacy label reads “Data Not Collected” because nothing is.

Free forever, Pro once

Pay once, or never.

The free tier is genuinely useful on its own. Pro is a single one-time purchase — not a subscription — and you can restore it on every device signed in to your Apple Account.

Free

A$0

  • 16-bit register decode
  • FLOAT32 in all four byte orders
  • The full address converter

FieldReg Pro

One‑time · price shown on the App Store

  • Wide decode — 32/64-bit integers and FLOAT64
  • Scale tools — linear + 4–20 mA loop
  • Bits & CRC and the full Reference library
  • Unlimited decode history and CSV export

Support

Questions & help

FieldReg is an offline Modbus/PLC register decoder and field-reference utility for iPhone, published by Aphelion Engineering. If you have a question, a bug report, or a feature request, email us and include your iPhone model and iOS version — we typically reply within a couple of business days.

Need a hand? Email bijan@aphelionengineering.com.au and we’ll get back to you.

Common questions

Does FieldReg work offline?
Yes — completely. Decoding, addressing, scaling, bit tools, CRC, and the reference library all work with no network connection, including in airplane mode and on first launch. The only feature that needs a connection is making or restoring an in-app purchase, which is handled by Apple.
I bought FieldReg Pro on another device (or reinstalled) — how do I get it back?
Open the app, go to the Pro/paywall screen, and tap Restore Purchases. As long as you’re signed in with the same Apple Account used for the original purchase, your Pro features unlock again. There’s no extra charge — Pro is a one-time purchase, not a subscription.
What does the Pro unlock include?
Wide decode (32/64-bit integers and FLOAT64), the Scale tools (linear + 4–20 mA loop), Bits & CRC, the full Reference library, unlimited decode history, and CSV export. The free tier always includes 16-bit decode, FLOAT32 in all four byte orders, and the address converter.
My purchase didn’t unlock / Restore says “no purchase found.”
First confirm you’re signed in to the same Apple Account that made the purchase, with a working network connection, then try Restore Purchases again. If it still doesn’t unlock, email us with your device model, iOS version, and the approximate purchase date and we’ll help.
Is my data private?
Yes. FieldReg collects nothing — no account, no analytics, no tracking. See the Privacy Policy for details.

FieldReg is made by Aphelion Engineering. Contact: bijan@aphelionengineering.com.au

Still stuck?

Email us your iPhone model and iOS version and we’ll sort it out.

Email support