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
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
Questions, or need a hand?
The support page covers restores, unlocks, and the common questions — or email us directly.