Hi all! Some questions...

Troy Sheets tsheets at saturn5.com
Tue Feb 10 20:52:19 CET 1998


> 
> 2) I'm starting to think about various MIDI hardware applications; I
> have some ideas about MIDI gadgets I'd like to build for myself. 
> I have the MIDI spec, but it doesn't say too much about the hardware
> besides the actual "signal interface" aspects.  I've never fooled
> with UARTs and unfortunately I forget sooooo much from the one digital
> lab I had involving microprocessors.  8P

There are some good books on the full MIDI spec if you look around for them...
I suggest university libraries.  Using a UART for midi is pretty simple
and streightforward.... and fun!  (it was a part of my senior project)

> My rough plan at the moment is to develop some MIDI gadget software
> in a CASE tool and get C code from it, which I would then run on
> either some sort of microcontroller or a more beefy chip depending
> on the complexity of the application.  What I'd like some advice on
> is how to handle the acquisition and decoding of the MIDI bit stream...
> I started to fool with designing the task of grabbing bit by bit from
> the stream, checking for start/stop bits, etc., right in the s/w, but
> I get the impression that a UART can be set up to do this for me, and
> then I get a ready-to-go byte-by-byte stream right from the UART.
> The UART is then somehow integrated with my microcontroller, micro-
> processor, or whatever, which is running the application software.

You sound like you know what you are doing.  Most UARTs have some 
configuration modes you can set to match the MIDI spec.  Then the UART 
coverts the MIDI serial bit stream into 8 bit bytes that interface with
your microcontroller.

> I have Hal Chamberlin's classic text, and it seems to give one example,
> but I was wondering if anyone has fooled with general (not "General")
> MIDI apps on any UART/processor combinations more modern than the 68K.
> I ask this since I'm worried about speed.  Unless, of course the 68K
> is beefy enough to handle anything MIDI wise.  Perhaps someone has 

Midi runs at something around 30 kilohertz, if I remember correctly.  This
is very slow compared to the speed of most microcontrolers... you should
not have a problem.

> some metrics on the subject?  I'm always reading about the sluggish
> MIDI response of this-or-that instrument in _Keyboard_ mag reviews;
> I wonder what causes the problem and why so many makers seem not to
> get around it.

One way to get around it to put each MIDI OUT connector on its own UART,
and then plug only 1 device into each MIDI OUT.  Sluggish midi performance
comes from trying to drive too many devices off a single MIDI bus.  If
you put each device on its own bus (with its own UART), you will probably
eliminate MIDI lag.

-troy

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