Comparison
CAN Bus, Modbus, RS485 and GPIO: Which One Your Equipment Uses
Updated 29 September 2026 · 6 min read
If you want to monitor plant and site equipment remotely, sooner or later you need to connect to it. The CAN bus vs Modbus question comes up often, along with RS485 and GPIO. This guide explains what each one is, which equipment typically uses it, and how a gateway reads them to get data into one place.
Why the connection type matters
Most modern equipment already knows a lot about itself. An engine control unit knows its hours, temperature and fault codes. A battery management system knows its state of charge. A pump controller knows whether it is running. The challenge is reading that information, and each type of equipment tends to use a different electrical connection and communication method.
Knowing which one your equipment uses tells you what data is available, what kind of device you need, and how much work the installation will involve.
CAN bus
CAN (Controller Area Network) bus was developed for vehicles and is now standard on most engines, machines and mobile plant. It is a shared two-wire network that lets the different electronic control units on a machine talk to each other. Every unit can send messages, and a device listening on the bus can read them without interrupting normal operation.
On diesel engines and heavy equipment, a common standard running over CAN is J1939, which defines how values such as engine speed, coolant temperature, fuel rate, running hours and fault codes are encoded. Other machines use manufacturer-specific messages, which may need decoding information from the manufacturer.
- Typical equipment: engines, excavators, dumpers, telehandlers, generator sets and other mobile plant.
- Strengths: rich machine data, robust in electrically noisy environments, designed for vehicles.
- Considerations: message formats vary between manufacturers, and connection points should be chosen carefully.
Modbus and RS485
RS485 is an electrical standard: a pair of wires that can carry data reliably over long cable runs, often hundreds of metres, with several devices on the same line. On its own it does not define what the data means.
Modbus is a simple communication protocol that does. One device, the master or client, asks another for the values held in numbered registers, such as a voltage or a status flag, and the other replies. Modbus RTU runs over serial links such as RS485. Modbus TCP carries the same idea over Ethernet networks. It is widely used in industrial and energy equipment because it is simple and well documented.
- Typical equipment: generator controllers, inverters, energy meters, battery management systems, pump controllers and environmental sensors.
- Strengths: open, widely supported, easy to read specific values once you have the register map.
- Considerations: you need the manufacturer's register map, and it is a request-and-reply protocol, so it is polled rather than continuous.
GPIO for simple signals
GPIO (general purpose input/output) is the simplest option: a wire that is either on or off, or carries a voltage that can be measured. It does not carry structured data, but it is often all you need.
Common uses include detecting ignition or engine running, reading a float switch in a sump, picking up an alarm contact from a controller, or sensing whether a door or hatch is open. GPIO is also useful on older equipment that has no data connection at all.
Inputs can be digital, reading on or off, or analogue, reading a voltage that represents something like a tank level. Check the voltage range the equipment produces against what the gateway input accepts, especially on 24V machines.
Practical questions before connecting
Before an installer visits, gathering a little information saves time and avoids a second trip. Manufacturers and dealers can usually supply most of it.
- Which interfaces does the equipment expose, and where are the connection points?
- For CAN bus, which standard or message set does it use, and at what speed?
- For Modbus, is a register map available, and what are the address and serial settings?
- For GPIO, what voltage does each signal use, and what does on or off mean?
- Is connecting third-party equipment permitted under the warranty or hire agreement?
CAN bus vs Modbus: side-by-side comparison
The table below summarises typical characteristics. Exact figures vary with cable, speed and installation, so treat them as general guidance.
| Factor | CAN bus | Modbus RTU (RS485) | Modbus TCP (Ethernet) | GPIO |
|---|---|---|---|---|
| What it is | Vehicle and machine network | Protocol over a serial line | Protocol over a network | Simple on/off or voltage input |
| How data flows | Units broadcast messages | Gateway polls registers | Gateway polls registers | Signal level is read directly |
| Typical equipment | Engines, plant ECUs, gensets | Controllers, meters, BMS, inverters | Networked controllers and meters | Ignition, float switches, alarm contacts |
| Data richness | High | Medium to high | Medium to high | Low (single state or value) |
| Typical cable reach | Tens of metres on a machine | Up to hundreds of metres | Up to around 100 m per copper segment | Short runs |
| What you need | Message definitions | Register map | Register map and IP address | Wiring and a signal description |
How a gateway uses them together
On a real site, one asset often uses more than one method. A hybrid generator might have an engine on CAN bus, a battery system on RS485 or Modbus, and an alarm output on a simple contact. A gateway with several interfaces can read each source, combine the values, and send them over cellular or Ethernet to a monitoring platform.
TrackSyte's Neo 2 gateway includes CAN bus, RS485, Modbus, GPIO and Ethernet on one 12V device, with LTE, LTE-M and NB-IoT cellular and GNSS, so one unit can cover the engine, the battery system and simple signals on the same asset. Data then appears in the TrackSyte Portal alongside the rest of the fleet.
FAQs
Is CAN bus better than Modbus?
Neither is better overall. CAN bus suits engines and machines, while Modbus suits controllers, meters and battery systems. The equipment you want to monitor usually decides which you use.
Is RS485 the same as Modbus?
No. RS485 is the electrical wiring standard and Modbus is a protocol that can run over it. Modbus can also run over Ethernet, and RS485 can carry other protocols.
What is J1939?
J1939 is a common standard that runs on CAN bus in diesel engines and heavy equipment. It defines how values such as engine speed, temperatures and fault codes are formatted.
Can I monitor equipment with no data connection?
Often, yes. GPIO inputs can read simple signals such as ignition, running status or alarm contacts, and external sensors can add readings such as fuel or water level.
Not sure what your equipment uses?
Tell TrackSyte what you need to monitor and we will help work out which connections are available and which gateway can read them.