From: Brian Candler <lists@...>
Date: 2012-12-27T07:14:56+09:00
Subject: Re: Comunication via rs485

iosu bueno wrote in post #1090230:
> Brian Candler wrote in post #1089866:
>> Google "ruby serial port"
>
> Im already using serialport gem in my project, but as they say in their
> page "Ruby/SerialPort is a Ruby library that provides a class for using
> RS-232 serial ports" so i dont know if I can use it to comunicate via
> rs485 or just rs232

Have you googled for the difference between RS232 and RS485? Also, you 
haven't said what hardware you want to use to connect your PC to RS485, 
nor what protocol you are going to use, nor what operating system you 
are using.

If this is just a long-reach point-to-point asynchronous serial link, 
then RS232 and RS485 are basically the same thing but with different 
electrical properties. If you are using an RS232-to-RS485 level shifter, 
or an RS485 card with a 16550A-compatible UART, then it will appear just 
like an RS232 serial port.

However if you are trying to do something cleverer, e.g. talk on an 
RS485 shared multipoint bus, you may have more work to do, e.g. turning 
the line driver on and off at the right times. This *might* still be 
drivable like an RS232 serial port, e.g. raising and lowering DTR might 
turn the transmit driver on and off. You'll need to read the 
documentation for the hardware and OS drivers you're using.

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