RS-485 protocol in ATMEGA168-15AD

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ghimiresharan

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Joined: Tue. Mar 2, 2021

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Posted by ghimiresharan: Tue. Apr 6, 2021 - 03:29 PM

Hello,

I am using ATMEGA168 Microcontroller and trying to get the hardware and pinout right for RS485 protocol. Is there a specific transceiver i have to choose so that there wont be any compatibility issue?

I have a sensor that uses RS485 so for that reason i need to use this protocol. Since RS485 is compatible with upto 32 devices i can just use 485 to intergrate with the pc and the sensor.

This is a rough sketch :

Can someone please let me know if this look correct? and those pins RO,/RE,DE and DI which ports should they connect to in microcontroller side?

Thanks.

- Sharan

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Learning and Information, General Electronics, Planet Analog, AVR DB

Last Edited: Tue. Apr 6, 2021 - 04:26 PM

ki0bk

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Posted by ki0bk: Tue. Apr 6, 2021 - 04:17 PM

Welcome to AVRFreaks!

This looks like normal half duplex serial comms, so the R0 pin connects to the USART pin rxd, the DI pin connects to USART pin txd, and the two direction pins (/RE and DE) are tied together and connects to any spare port pin and you control it so it is low for receiving data, and high when transmitting data. You will want to set TX direction, and then call your usart transmit function (usually putc() or puts()) wait for the TXC flag is set, saying all data has been transmitted, then and only then set the direction pin low to receive replies.

Jim

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ghimiresharan

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Posted by ghimiresharan: Tue. Apr 6, 2021 - 06:25 PM

Are there any compatibility issue with transceiver or can i use any ttl to 485 module with any microcontroller?

- Sharan

ki0bk

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Posted by ki0bk: Tue. Apr 6, 2021 - 07:00 PM

they all work!

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MurdoMcLeod

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Posted by MurdoMcLeod: Sat. Apr 10, 2021 - 09:43 AM

Well the usual electronics caveat applies - check the voltage levels. Some RS485 transceivers only work from 5v, and some can work from 3v to 5v. Also, when working from 5v some won’t accept 3V3 signals. And if the transceiver is working from 5v it will spit out 5v on the receive line which a 3v3 micro might not like. If everything is TTL level voltages ie 5v then you will be fine.

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