Glossary

Plain-words definitions for the ISOBUS, J1939, NMEA, and machbus terms used throughout this book. Definitions are written in the book’s own words and aim to match how each idea is used in the surrounding pages. Where a topic has a dedicated chapter, a “(see …)” pointer is given.

A

Address claim — The handshake by which a device tells the bus it intends to use a particular one-byte address, and defends that choice against any other device that wants the same address. (see NAME and address claim)

AEF — Agricultural Industry Electronics Foundation, the group that runs the interoperability test and certification program for ISOBUS products. machbus ships no AEF certification.

Alarm mask — A Virtual Terminal screen layout that the operator’s terminal shows when a working set raises an alarm, typically grabbing attention and optionally sounding the terminal. (see Virtual Terminal concepts)

Arbitration — The mechanism on a CAN bus that decides which message goes first when two devices transmit at once: the lower identifier wins, bit by bit, without corrupting either frame. The same idea decides address-claim contests.

B

BAM — Broadcast Announce Message: the transport mode that sends a large message to everyone on the bus, one numbered chunk at a time, with no handshake or flow control. (see Transport Protocol)

Broadcast address — The destination value (255) meaning “every device on the bus.” A message addressed there is for all listeners rather than one partner.

C

CAN — Controller Area Network: the low-level serial bus that carries every ISOBUS and J1939 frame. It provides short frames, built-in priority, and collision-free arbitration. (see CAN and J1939)

CMDT — Connection-mode data transfer: the handshaked transport mode that moves a large message to a single destination using request-to-send and clear-to-send exchanges. (see Transport Protocol)

Commanded address — A network management instruction that tells a specific device (identified by its NAME) to move to a new address. The device obeys and re-claims at the commanded value. (see NAME and address claim)

Control function (CF) — Any addressable participant on the bus: a logical sender/receiver identified by a NAME and an address. One physical box can host several control functions.

CTS — Clear To Send: the receiver’s reply in a handshaked transport that tells the sender how many chunks it may send next, and from which point. (see Transport Protocol)

D

DDI — Data Dictionary Identifier: a standardized code naming one quantity a device can report or accept, such as an application rate or a section state. DDIs make process data portable across vendors. (see DDOP and process data)

DDOP — Device Descriptor Object Pool: the structured self-description an implement uploads to a Task Controller, listing its elements, the quantities it exposes, and how to present them. (see DDOP and process data)

Device element — One node in a DDOP tree that represents a real or logical part of the machine (the whole device, a boom, a single section) and carries the process-data quantities tied to that part. (see DDOP and process data)

DTC — Diagnostic Trouble Code: a fault report combining a parameter number and a failure-mode code, used to surface problems to operators and tools. (see Diagnostics basics)

E

ECU — Electronic Control Unit: a physical computing box on the machine. An ECU may host one or more control functions.

EOM — End-of-message acknowledgement: the receiver’s confirmation, after a handshaked transport, that it got every chunk and reassembled the whole message.

ETP — Extended Transport Protocol: the transport used for messages too large for the ordinary transport protocol, using larger sequence numbers and byte-offset bookkeeping. (see Transport Protocol)

F

Fast Packet — The NMEA 2000 multi-frame scheme that strings several CAN frames together to carry a single larger marine/navigation message. (see NMEA and GNSS basics)

Fix quality — The reported trustworthiness of a GNSS position, distinguishing no fix, a basic fix, and corrected high-accuracy modes. Guidance and section control care a great deal about this value. (see NMEA and GNSS basics)

FMI — Failure Mode Identifier: the code that says how a parameter is failing (too high, too low, open circuit, and so on) inside a fault report.

FS — File Server: a device that offers shared storage on the bus so other control functions can read and write files. (see File Server and large data)

G

GNSS — Global Navigation Satellite System: the umbrella term for satellite positioning (GPS and its peers) that feeds position, speed, and heading into guidance and mapping. (see NMEA and GNSS basics)

I

Identifier (29-bit) — The extended CAN frame header that ISOBUS uses. It packs priority, the parameter group, the destination (when applicable), and the source address into one value that also decides arbitration order. (see PGNs, priority, source, destination)

Industry group — A field inside a NAME that says which family of machinery the device belongs to (for example, agricultural equipment), helping classify participants on a shared bus.

Internal vs partner CF — From your stack’s viewpoint, an internal control function is one your own code owns and operates; a partner control function is another device you have chosen to talk to. The distinction drives filtering and routing. (see Control functions and partners)

ISB (Shortcut Button) — The ISOBUS Shortcut Button: a single operator control whose press commands every listening implement to drop into a safe, stopped state. (see Shortcut Button and safe-state thinking)

ISOBUS — The agricultural networking standard defined by the ISO 11783 family of parts, built on top of J1939, that lets tractors, implements, and terminals from different makers interoperate.

M

Manufacturer code — A field in a NAME identifying which company made the device, assigned so that NAMEs stay globally distinct.

Mask (data / alarm / soft key) — A Virtual Terminal screen region. The data mask is the main working area an implement draws into, the alarm mask interrupts with a warning, and the soft key mask holds the row of programmable buttons. (see Virtual Terminal concepts)

N

NAME — The 64-bit identity of a control function. It encodes who made it, what function it performs, its industry group, and whether it can move its own address; its numeric value also sets priority in address-claim contests. (see NAME and address claim)

NIU / router — Network Interconnection Unit: a node that bridges two CAN segments, forwarding the traffic that belongs across the boundary. In machbus the routing layer plays this role. (see Network routing)

NMEA — The marine-electronics body behind the NMEA 0183 serial sentences and the CAN-based NMEA 2000 messages, several of which carry the GNSS and navigation data ISOBUS machines consume. (see NMEA and GNSS basics)

Null address — The placeholder source address (254) a device uses while it has no valid claimed address, for example after losing an address contest. A device at the null address cannot do normal traffic.

O

Object pool — The bundle of drawing and interaction objects a Virtual Terminal client uploads so the terminal can render and run its user interface. (see Working sets and object pools)

ObjectID — The numeric handle that names one object inside an object pool, so later messages can reference, change, or read that exact object. (see VT object pools)

P

PDU1 / PDU2 — Two header formats for a parameter group. PDU1 carries a destination address (a directed message to one device), while PDU2 has no destination field and is always broadcast. (see PGNs, priority, source, destination)

PGN — Parameter Group Number: the identifier of a kind of message, telling you what the payload means regardless of who sent it. (see PGNs, priority, source, destination)

Priority — The few header bits that bias arbitration: lower-numbered priority wins the bus sooner, so urgent messages can preempt routine ones. (see PGNs, priority, source, destination)

Process data — The live, named quantities an implement and a Task Controller exchange during work: measured values flowing up and setpoints flowing down, each tagged by a DDI. (see DDOP and process data)

R

RTS — Request To Send: the opening message of a handshaked transport, naming the message to come and its size so the receiver can agree to take it. (see Transport Protocol)

S

Safe state — The defined, predictable condition a device falls back to when something goes wrong or an operator demands a stop: outputs off, motion halted, no surprises. (see Shortcut Button and safe-state thinking)

SC — Sequence Control (and, by extension, section control work): the mechanism for running ordered, scripted automation steps between cooperating devices. (see Sequence Control and TIM)

Section control — Automatically switching individual implement sections on and off based on position, coverage, and boundaries, so you avoid double-applying or treating outside the field. (see Task Controller concepts)

Self-configurable address — A flag in a NAME marking a device that is allowed to pick a different address on its own if its first choice is taken. Devices without it must keep a fixed address. (see NAME and address claim)

Sequence control — See SC: coordinated, step-by-step command sequences between an initiator and the devices it drives. (see Sequence Control and TIM)

Setpoint — A target value a controller asks an implement to achieve, such as a commanded application rate, expressed as process data. (see DDOP and process data)

Soft key — A programmable on-screen button on a Virtual Terminal whose meaning is defined by the current object pool and whose presses are reported back to the working set. (see Virtual Terminal concepts)

Source address — The one-byte field in every frame saying which control function sent it. A device must own a claimed address before using it as a source. (see PGNs, priority, source, destination)

SPN — Suspect Parameter Number: the code naming which parameter a fault report is about. Paired with an FMI it identifies a specific problem.

T

TAN — Transaction number: a small rolling counter carried in some Virtual Terminal exchanges so a request and its matching response can be paired unambiguously. (see VT updates)

TC — Task Controller: the device that drives documentation and control of field work, receiving process data, applying prescriptions, and coordinating section control with implements. (see Task Controller concepts)

TECU — Tractor ECU: the tractor-side control function that publishes machine data (speed, distance, power-takeoff, hitch, and similar) for implements to use. (see Tractor ECU)

TIM — Tractor Implement Management: the framework that lets an approved implement request limited control over tractor functions, under operator oversight and safety conditions. (see Sequence Control and TIM)

Transport protocol — The set of rules for splitting a message larger than one CAN frame into numbered chunks and reassembling them, whether broadcast (BAM) or handshaked (CMDT). (see Transport Protocol)

V

Value presentation — The formatting metadata in a DDOP that says how to turn a raw process-data number into something human-readable: scale, offset, decimal places, and units. (see DDOP and process data)

VT — Virtual Terminal: the shared operator display in the cab that renders the user interface uploaded by each implement and reports operator input back to it. (see Virtual Terminal concepts)

W

Working set — The identity an implement presents to services such as the Virtual Terminal: a root object that groups the device’s interface and its member control functions. (see Working sets and object pools)

Working-set master — The control function that speaks for a working set, performing the upload and interaction handshakes on behalf of any members behind it. (see Working sets and object pools)

Reminder: these definitions explain how the book uses each term. machbus carries no ISO, SAE, NMEA, or AEF certification; real deployment still requires the official standards, hardware, and interoperability evidence.