Multiple Micro-Ros MCUs over the same serial

asked 2021-09-03 07:57:49 -0500

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Hello,

From what I have seen, there is some example of Micro-ros over serial. But all I have seen is one computer (or one MCU) communicating to one MCU.

I was wondering if it was possible for example to connect two MCUs on the same serial lines to one computer? So the computer would have only one serial port to communicate with two different MCUs (or even more!).

I know that Modbus-RTU allows to do this, but it's a rather old protocol that doesn't allow much flexibility. If it's not possible to use multiple MCUs on the same serial lines with Micro-ros, is there a way to build a multiple MCUs architecture without duplicating the serial port on the computer?

Thanks.

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answered 2021-09-07 02:19:32 -0500

Pablogs
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In general, a bare UART serial port (same Tx and Rx lines) cannot be shared by multiple devices since it does not have medium access control.

You have the possibility of connecting multiple MCU to a single micro-ROS Agent using a serial port for each MCU using the multiserial Agent feature. You will need to use something like:

ros2 run micro_ros_agent micro_ros_agent multiserial [args]

If you want to use a serial communication device that allows address and multidevice medium access (SPI, RS485...) you can create your own micro-ROS transports for both Client and Agent, please check this tutorial.

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answered 2021-09-04 02:44:44 -0500

mbudris
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There are ways to do this, but none of them are ROS related. If by "serial" you refering to rs232 , then the possibilities are limited and comes with the "if you know what you're doing" warning.

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By serial, I mean the UART of the MCUs (It could be only UART, rs232 or rs485 etc.). What are the possibilities, then? RS-485 allows multidrop-communication is there anything that would be more modern than ModBus RTU (modbus is limited to 16 bit data)?

GuillaumeB ( 2021-09-04 06:02:08 -0500 )edit

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