LinuxGuru
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Re: GPIO I2S/KNX/Modbus Port Expanders

Fri Mar 09, 2012 10:46 pm

Hi all,

Anyone have any info about GPIO I2S / KNX / Modbus port expanders for RPi and availability of related kernel modules?

Thanks in advance for any suggestion(s).

kasperl
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Re: GPIO I2S/KNX/Modbus Port Expanders

Sat Mar 10, 2012 8:09 am

I2S will probably be a soldering hack. Do a google for I2S Gert soldering and you'll probably find it at some point.

KNX I know nothing about, so I hope someone else can answer that.

Modbus: Depends. I know there's a serial and a ethernet spec, so it kind of depends on which you mean. Modbus over ethernet will work, and there's plenty of Python code available on the internet to talk with the PLC's. It works, but timing can be fiddly if you use to serial port module on the modbus to talk with something time-sensitive. As for serial, you've got UART, which can be converted to RS232 with the appropriate level converters. However, you haven't got hardware handshaking, there's no RTS or CTS brought out onto the GPIO. You can get a normal USB to RS232 dongle, most work with Linux.

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TonyD
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Re: GPIO I2S/KNX/Modbus Port Expanders

Mon Mar 12, 2012 2:11 pm

As already said, Modbus comes in two flavours, Ethernet and Serial. Hardware wise you can either use the Ethernet port from the Model B for the Ethernet version or use the UART from the expansion interface with a level changer for either RS232 (MAX3232) or RS485 (MAX3072) for the serial version. I've already done a simple RS232 breakout board. see here

Software wise theres quite a few free (open source?) Modus stacks out there. FreeMODBUS is targeted for several different micros, but I'm guessing a Linux based stack would be best for the RPi.
Tony

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csoutreach
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Re: GPIO I2S/KNX/Modbus Port Expanders

Mon Mar 19, 2012 6:55 pm

LinuxGuru said:


Hi all,

Anyone have any info about GPIO I2S / KNX / Modbus port expanders for RPi and availability of related kernel modules?


Details of Kernel drivers here

http://www.raspberrypi.org/for.....8;search=1
http://piface.openlx.org.uk/ Raspberry Pi IO Interface Board

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