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Michael Karas
02/16/12 10:46
Read: 676 times
Beaverton Or

#186030 - RS485 Confused With MIDI
Responding to: Erik Malund's previous message
I agree with Erik that the standard termination of a RS485 network puts the termination at both ends of the daisy chain wiring for the network. Since a typical RS485 device is designed to be able to be connected in daisy chain manner from device to device it can be rather inconvenient to embed the termination onto a particular device. Doing so means that there needs to be some means to disconnecct the termination within any device that ends up not being at the ends of the daisy chain.

On the other hand MIDI connectivity is a point to point topology. MIDI devices have specific IN and separate OUT connectors. They also often have a THRU connector that bridges from an IN for direct traffic flow through a device.

When Chico proposes to substitute RS485 signalling for MIDI he will not be using the daisy chain multi-drop type bidirectional interface that is the usual for a RS485 network. Instead he will using it in unidirectional point to point connection. When used like this there is absolutely no reason that the terminators cannot be placed within the MIDI OUT device and also at the corresponding MIDI IN device port.

I tend to agree with Kai in this discussion in that it makes little sense to go down this road of using RS485 signalling as a substitute for MIDI standard connectivity. Standard MIDI connections are opto coupled to prevent ground loop connections between pieces of audio equipment. This is extremely important in the audio realm because a small amount of ground coupling can introduce large amounts of 50/60 Hz noise into the audio at the analog ports of the system. On top of that MIDI connections are a current loop type of interface that is much more tolerant of running longer distances than a voltage signalling interface.

Chico's apparent difficulty of purchasing standard MIDI connectors and thus proposing to switch over to some other scheme with different connectors and signalling, while maybe feasible, seems to be a wrong direction to go.

Michael Karas

List of 25 messages in thread
MIDI through rs485      Chico Magalh„es      02/13/12 22:48      
   In a closed environment...        Michael Karas      02/14/12 06:38      
      Bridge      Per Westermark      02/14/12 07:25      
      That's the point      Chico Magalh„es      02/14/12 11:42      
   Why?      Kai Klaas      02/14/12 08:19      
   It is getting very hard get MIDI conectors        Andy Neil      02/14/12 09:23      
      Being a standard...      Kai Klaas      02/14/12 12:33      
      I agree      Chico Magalh„es      02/14/12 18:26      
         daisy-chain      Andy Neil      02/15/12 01:00      
            Thank you.      Chico Magalh„es      02/15/12 12:41      
            485 is not a good choice for "mobile use"      Erik Malund      02/15/12 12:46      
               Isnt same as DMX?      Chico Magalh„es      02/15/12 12:53      
                  no      Erik Malund      02/15/12 13:21      
                     Terminator together with the "sender"?      Chico Magalh„es      02/16/12 00:17      
                        No, absolutely not      Erik Malund      02/16/12 07:07      
                           RS485 Confused With MIDI      Michael Karas      02/16/12 10:46      
                              which begs a question      Erik Malund      02/16/12 10:54      
                                 Sounded more like mixing DMX/MIDI on same cable      Per Westermark      02/16/12 11:04      
                                    Wrong...      Chico Magalh„es      02/16/12 12:43      
                                 MIDI stays...      Chico Magalh„es      02/16/12 12:48      
   Look here...      Kai Klaas      02/15/12 09:27      
      Good one...      Chico Magalh„es      02/15/12 12:42      
         Only an example...      Kai Klaas      02/15/12 13:56      
            not surprising      Erik Malund      02/15/12 14:06      
            one of the cheapest you can buy      Andy Neil      02/15/12 15:59      

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