# Configuration syntax for 'Serial port' in Modbus RTU driver

**URL:** <https://forum.inductiveautomation.com/t/configuration-syntax-for-serial-port-in-modbus-rtu-driver/26258>\
**Category:** Ignition\
**Created:** [July 3, 2019, 10:59am UTC](https://forum.inductiveautomation.com/t/configuration-syntax-for-serial-port-in-modbus-rtu-driver/26258 "2019-07-03T10:59:59Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![chris.roys](https://avatars.discourse-cdn.com/v4/letter/c/e9c0ed/32.png) [@chris.roys](https://forum.inductiveautomation.com/u/chris.roys)\
**Post date:** [July 3, 2019, 10:59am UTC](https://forum.inductiveautomation.com/t/configuration-syntax-for-serial-port-in-modbus-rtu-driver/26258/1 "2019-07-03T10:59:59Z")

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Hello  
What is the current format & syntax for configuration of ‘Serial port’ in Modbus RTU driver? For example COM1, COM01,…

There is no help file for that?

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/b/b21777f952b5cddb55e7e4f6f6b9f9c044340a98.png)

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**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [July 3, 2019, 12:07pm UTC](https://forum.inductiveautomation.com/t/configuration-syntax-for-serial-port-in-modbus-rtu-driver/26258/2 "2019-07-03T12:07:36Z")

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It varies with platform. For my systems, it typically will be /dev/ttyS0 or similar. Generally you use what your OS expects. Since the modbus driver is delegating to the serial support module, you might want to look at its documentation, like [system.serial.openSerialPort()](https://docs.inductiveautomation.com/display/DOC79/system.serial.openSerialPort).