Understanding the MIDI Specification Circuit

Discussion in 'General Electronics Chat' started by boingaon, Jan 6, 2013.

  1. boingaon

    Thread Starter Member

    May 15, 2012
    31
    0
    Hello,

    I'm developing a product that has MIDI functionality built into it. There are some aspects of the MIDI specification that are unclear to me.

    [​IMG]

    1. Those dotted circles are apparently indicating ground of some sort. Does this simply show that those nodes are connected together to ground?

    2. Is this a UART connection that is sent from the input to the onboard microcontroller of the MIDI controller?

    3. A blank triangle with a circle on the tip?

    4. This one has an A inside...

    5. Why didn't they specify the type/stats for the opto-isolator?

    -Thx
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Last edited: Jan 6, 2013
  3. boingaon

    Thread Starter Member

    May 15, 2012
    31
    0
    1. How can you use 2-con shielded cable if this circuit will be put on a PCB?

    2. MIDI is sent as bits in serial form. Why would the line need to be converted from DC to AC using an inverter? (Also they don't give specs for the inverter).

    3. Does the dotted circle only apply to wires that the circle encloses? What about the large dotted rectangle?
     
  4. boingaon

    Thread Starter Member

    May 15, 2012
    31
    0
    Thanks for both of those links.
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    1. The drawing assumes remote mounted jacks. You don't need shielded cable if mounting the jacks close to the IC's on a PCB.

    2. The inverter in this context is a logic inverter IC not a power supply inverter.

    Carefully read the attached link's :)

    3. Yes. The rectangle outlines an optional circuit.
     
    Last edited: Jan 6, 2013
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    The A in the second inverter probably means inverting amplifier.
     
  7. boingaon

    Thread Starter Member

    May 15, 2012
    31
    0
    That makes sense. "1" equals digital low, and "0" equals digital high in MIDI, so the inverter does this conversion.
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    The inversion is not needed, the diagram shows two inverters becuase they are suggestion the use of a digital buffer.

    Modern micros have good CMOS outputs and can drive the MIDI output directly, but old TTL logic chips etc needed a buffer.
     
Loading...