# Modbus TCP

Protocols · `Modbus-TCP` · verification: source checked

Modbus TCP carries the Modbus application protocol over TCP/IP. A client sends a request naming a function code and a register or coil address, and the server replies with the data or an exception code. It has no built-in authentication in its original form.

## Specification

| Property | Value |
|---|---|
| Transports | tcp |
| Architecture | client server |
| Encoding | binary |

### Default ports

| Port | Transport | Secure | Purpose |
|---|---|---|---|
| 502 | tcp | false | Modbus Application Protocol |
| 802 | tcp | true | Modbus Application Protocol Secure |

## Connected

- Related: [Modbus.org Modbus/TCP Security](https://machineschema.com/protocol/modbus-security.md)
- Supported by: [AutomationDirect C-more CM5-T12W](https://machineschema.com/hardware/automationdirect-cm5-t12w.md), [AutomationDirect EA3-S3ML](https://machineschema.com/hardware/automationdirect-ea3-s3ml.md), [AutomationDirect EA3-T4CL](https://machineschema.com/hardware/automationdirect-ea3-t4cl.md), [AutomationDirect Productivity2000](https://machineschema.com/controller/automationdirect-productivity2000.md), [Beckhoff CX8090](https://machineschema.com/hardware/beckhoff-cx8090.md), [Beckhoff CX8110](https://machineschema.com/hardware/beckhoff-cx8110.md), [Beckhoff CX8180](https://machineschema.com/hardware/beckhoff-cx8180.md), [Beckhoff CX8190](https://machineschema.com/hardware/beckhoff-cx8190.md), [Beckhoff CX8191](https://machineschema.com/hardware/beckhoff-cx8191.md), [Comau MyCo-10-1.00](https://machineschema.com/hardware/comau-myco-10-1-00.md), [Comau MyCo-15-1.30](https://machineschema.com/hardware/comau-myco-15-1-30.md), [Comau MyCo-3-0.59](https://machineschema.com/hardware/comau-myco-3-0-59.md), [Comau MyCo-3-0.95](https://machineschema.com/hardware/comau-myco-3-0-95.md), [Comau MyCo-5-0.80](https://machineschema.com/hardware/comau-myco-5-0-80.md), [DOBOT Magician E6](https://machineschema.com/hardware/dobot-magician-e6.md), [DOBOT Nova 2](https://machineschema.com/hardware/dobot-nova-2.md), [Dobot CR 30H-Food](https://machineschema.com/hardware/dobot-cr-30h-food.md), [Dobot M1 Pro](https://machineschema.com/hardware/dobot-m1-pro.md), [Dobot MG400](https://machineschema.com/hardware/dobot-mg400.md), [Dobot Nova 5](https://machineschema.com/hardware/dobot-nova-5.md), [Elite Robots CS530H](https://machineschema.com/hardware/elite-robots-cs530h.md), [Elite Robots CS612](https://machineschema.com/hardware/elite-robots-cs612.md), [Elite Robots CS620](https://machineschema.com/hardware/elite-robots-cs620.md), [Elite Robots CS630](https://machineschema.com/hardware/elite-robots-cs630.md), [Flexiv Hesper](https://machineschema.com/hardware/flexiv-hesper.md), [Franka Robotics Franka Research 3](https://machineschema.com/hardware/franka-robotics-franka-research-3.md), [JAKA 12 kg collaborative robot](https://machineschema.com/hardware/jaka-collaborative-robot-12kg.md), [JAKA C5](https://machineschema.com/hardware/jaka-c5.md), [JAKA CAB 16](https://machineschema.com/hardware/jaka-cab-16.md), [JAKA CAB 7](https://machineschema.com/hardware/jaka-cab-7.md), [JAKA MiniCab](https://machineschema.com/hardware/jaka-minicab.md), [JAKA MiniCobo](https://machineschema.com/hardware/jaka-minicobo.md), [JAKA Zu 12](https://machineschema.com/hardware/jaka-zu-12.md), [JAKA Zu 18](https://machineschema.com/hardware/jaka-zu-18.md), [JAKA Zu 3](https://machineschema.com/hardware/jaka-zu-3.md), [JAKA Zu 30](https://machineschema.com/hardware/jaka-zu-30.md), [JAKA Zu 7](https://machineschema.com/hardware/jaka-zu-7.md), [JAKA Zu series](https://machineschema.com/hardware/jaka-zu-series.md), [JAKA Zu35](https://machineschema.com/hardware/jaka-zu35.md), [Universal Robots UR10e](https://machineschema.com/hardware/universal-robots-ur10e.md), [Universal Robots UR12e](https://machineschema.com/hardware/universal-robots-ur12e.md), [Universal Robots UR12e-1300](https://machineschema.com/hardware/universal-robots-ur12e-1300.md), [Universal Robots UR15](https://machineschema.com/hardware/universal-robots-ur15.md), [Universal Robots UR16e](https://machineschema.com/hardware/universal-robots-ur16e.md), [Universal Robots UR18](https://machineschema.com/hardware/universal-robots-ur18.md), [Universal Robots UR20](https://machineschema.com/hardware/universal-robots-ur20.md), [Universal Robots UR20-1750](https://machineschema.com/hardware/universal-robots-ur20-1750.md), [Universal Robots UR30](https://machineschema.com/hardware/universal-robots-ur30.md), [Universal Robots UR30-1300](https://machineschema.com/hardware/universal-robots-ur30-1300.md), [Universal Robots UR3e](https://machineschema.com/hardware/universal-robots-ur3e.md), [Universal Robots UR5e](https://machineschema.com/hardware/universal-robots-ur5e.md), [Universal Robots UR7e](https://machineschema.com/hardware/universal-robots-ur7e.md), [Universal Robots UR7e-920](https://machineschema.com/hardware/universal-robots-ur7e-920.md), [Universal Robots UR8 Long](https://machineschema.com/hardware/universal-robots-ur8-long.md), [Universal Robots e-Series Control Box](https://machineschema.com/controller/universal-robots-e-series-control-box.md)

## Safety

- Plain Modbus TCP has no authentication or encryption. Anyone who can reach port 502 can write holding registers, so keep it on an isolated OT network.

## Study notes

- Data lives in four tables: coils (1-bit read/write), discrete inputs (1-bit read-only), input registers (16-bit read-only) and holding registers (16-bit read/write).
- Each request carries an MBAP header with a transaction id, so a client can match replies to requests.

## Sources

1. [IANA Service Name and Transport Protocol Port Number Registry (mbap, mbap-s)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=mbap) (accessed 2026-10-25)
2. [Modbus Organization: Modbus specifications](https://www.modbus.org/modbus-specifications) (accessed 2026-10-25)

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JSON: https://machineschema.com/protocol/modbus-tcp.json  
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite Machine Schema and the original sources.