Please provide a link to the modbus library you use. This is where I found the information I saw about RTU on RS-485 board
https://www.arduino.cc/en/ArduinoModbus/ArduinoModbus On Mon, Oct 26, 2020 at 11:11 AM John Vaughters via TriEmbed < [email protected]> wrote: > oh, forgot to mention the Pi 3.3v Tx -> ard Rx is just accepted via > threshold limits and therefore is just a direct connect. > > > > > > > On Monday, October 26, 2020, 11:08:57 AM EDT, John Vaughters via TriEmbed < > [email protected]> wrote: > > > > > > Rodney, > > There are a number of modbus libraries out there, so I'm not sure which > one you are referring to. Yes, when I said UART, I specifically meant TTL. > I use a very simple voltage divider for the ard Tx -> Pi Rx with one > resister value and 3 resistors. I think I have used both 10k and 1k ohms > and parallel two resistors to get half the value and series the third > resistor. This gives you a super simple interface to the arduino that is 5V > -> 3.3 Pi. I use the 5V pin of the Pi to power the 5v pin of the arduino. > GND common of course. I use the simple-modbus Library code and I hesitate > to give you a link, because in doing a quick search, I am not sure which > code I am currently using, but the concept of this library is to use a very > minimal set of modbus functions with holding registers only. This can be > used to gang bits into a single register for binary, if I remember > correctly. Thinking from the top of my head, so check that. I think you > will find a couple forks of the original simple-modbus. Then I pass it onto > mbusd to convert it TCP. So the serial is MODBUS RTU and mbusd converts it > to MODBUS TCP. > > What I like about this config and have been using it for a couple years is > it is super reliable. UART being one of the oldest most reliable comms and > MODBUS being one of the oldest most reliable industrial protocols, it makes > for a a very reliable and recoverable from hard reboot combination. > However, there are even more complete modbus libraries that I have used in > the past, but simple-modbus, well..... is simple :) > > John Vaughters > > > > > > > On Monday, October 26, 2020, 10:23:19 AM EDT, Rodney Radford < > [email protected]> wrote: > > > > > > I have not used the modbus Arduino code before, but it does look > interesting. However in reading the description they state it is designed > to use with either their Ethernet shield or the RS485 shield, but I did not > see anything on running it with just a standalone Arduino. If it is > possible to just use the TTL serial port of the Arduino, that would be very > nice, indeed. > > _______________________________________________ > Triangle, NC Embedded Computing mailing list > > To post message: [email protected] > List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > TriEmbed web site: http://TriEmbed.org > To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > > > _______________________________________________ > Triangle, NC Embedded Computing mailing list > > To post message: [email protected] > List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > TriEmbed web site: http://TriEmbed.org > To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > >
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