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'[PIC]: MIDI handling. where to start?'
2003\02\26@114619 by faisal moro

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hi there

here's the reason why i (just) started learning PICs: MIDI handling.
I'd need some advice, inputs, to start learning.

any help appreciated

tia
Faisal

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2003\02\26@130250 by Byron A Jeff

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On Wed, Feb 26, 2003 at 05:44:23PM +0100, faisal moro wrote:
> hi there

Hi.

>
> here's the reason why i (just) started learning PICs: MIDI handling.
> I'd need some advice, inputs, to start learning.

MIDI isn't really that hard. I call it easy by design. The hardware is a
simple current loop that signals serially at 31250 BPS with a standard 8N1
format. The seemingly odd bit rate matches well with standard microcontroller
frequencies because it's exactly 1/32 of 1 Mhz so it's easy to generate
exactly.

A bried rundown can be found here:

http://stage.itp.nyu.edu/~tigoe/pcomp/midi.shtml

BAJ

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2003\02\27@023556 by Roman Black

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Byron A Jeff wrote:

> MIDI isn't really that hard. I call it easy by design. The hardware is a
> simple current loop that signals serially at 31250 BPS with a standard 8N1
> format. The seemingly odd bit rate matches well with standard microcontroller
> frequencies because it's exactly 1/32 of 1 Mhz so it's easy to generate
> exactly.
>
> A bried rundown can be found here:
>
> http://stage.itp.nyu.edu/~tigoe/pcomp/midi.shtml


It will require an optocoupler, and a FAST one.
A recent kit here specified a fast opto as they
experienced problems with some slower optos even
though it was "in spec." I'd allow a healthy
margin for opto speed if it is a known problem.
:o)
-Roman

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2003\02\27@034259 by Neil Bradley

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> > simple current loop that signals serially at 31250 BPS with a standard 8N1
> > format. The seemingly odd bit rate matches well with standard microcontroller
> > frequencies because it's exactly 1/32 of 1 Mhz so it's easy to generate
> > exactly.
> It will require an optocoupler, and a FAST one.

Speaking as someone who lives, eats, and breathes MIDI, the hardware
surrounding it and the micros involved in it, the Sharp PC900s, HP 6N138s,
and the CNY17s aren't all that fast and they work flawlessly, and are even
recommended by the MIDI manufacturers association. The reference
implementation published just about everywhere is found here:

http://www.borg.com/~jglatt/tech/midispec/hardware.htm

For those interested, the MIDI baud rate was selected because of its ease
of implementation in the CPU used in the original Sequential Circuits
Prophet 600. If you want to go further back, MIDI was actually born in the
remote Prophet - a remote keyboard for the Prophet 5 that spoke a very
primitive version of MIDI.

It used an 8051 CPU, clocked at 12Mhz. The clock circuit is /12, then fed
to a /16 for the baud rate generator, then a /2 option was set in the
MCS-51 family's UART. 1200000/12=1000000/16=62500/2=31250kpbs. If you want
to stay compatible with all MIDI devices, keep your % of error at 1% or
under.

-->Neil

-------------------------------------------------------------------------------
Neil Bradley            In the land of the blind, the one eyed man is not
Synthcom Systems, Inc.  king - he's a prisoner.
ICQ #29402898

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2003\02\27@044836 by faisal moro

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thanks guys

loads of resources on your links!
besides, as i'm going to build a midi footcontroller, i don't need
any MIDI IN capabilities. this makes things easier uh?
i just need to send program change and control change commands
(on/off, 0/127) when recalling a memory location on the pedalboard,
and use a couple of expression pedals to send continous controls
(from 0 to 127).

[i'll considerin MIDI IN later, maybe to link 2 pedalboards together]

thanks
Faisal

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2003\02\27@094732 by ?iso-8859-1?Q?Per_Linn=E9?=

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----- Original Message -----
From: "Neil Bradley" <spam_OUTnbTakeThisOuTspamSYNTHCOM.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Thursday, February 27, 2003 9:40 AM
Subject: Re: [PIC]: MIDI handling. where to start?


>
> remote Prophet - a remote keyboard for the Prophet 5 that spoke a very
> primitive version of MIDI.
>
No, almost totally wrong! The only resemblance it has with MIDI
is that it is a serial interface. And not even that is entirely correct,
'cause the Prophet-5 interface is synchronous. There is a separate
clock signal in the cable. Besides it sends the entire keyboard map
instead of the event concept MIDI utilizes. (Note On, Note Off etc.)

PerL

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2003\02\27@105449 by fred jones

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We're having to dig deep here cause this was a long time ago but I believe
that Sequential was trying to jump the gun on the Prophet 5 and implemented
a "MIDI" port before the standard was finalized so it was not what was
actually decided upon.  I don't know if the book is still available but back
in 1985, about 2 years after the MIDI spec was published, I bought a book by
Craig Anderton that had enough detail that I was able to implement hardware
and code on a C64 computer.
FJ






>From: Per Linni <per.linnespamKILLspamSWIPNET.SE>
>Reply-To: pic microcontroller discussion list <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
>To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
>Subject: Re: [PIC]: MIDI handling. where to start?
>Date: Thu, 27 Feb 2003 15:45:44 +0100
>
>{Original Message removed}

2003\02\27@105703 by Byron A Jeff

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On Thu, Feb 27, 2003 at 06:19:32PM +1100, Roman Black wrote:
> Byron A Jeff wrote:
>
> > MIDI isn't really that hard. I call it easy by design. The hardware is a
> > simple current loop that signals serially at 31250 BPS with a standard 8N1
> > format. The seemingly odd bit rate matches well with standard microcontroller
> > frequencies because it's exactly 1/32 of 1 Mhz so it's easy to generate
> > exactly.
> >
> > A bried rundown can be found here:
> >
> > http://stage.itp.nyu.edu/~tigoe/pcomp/midi.shtml
>
>
> It will require an optocoupler, and a FAST one.
> A recent kit here specified a fast opto as they
> experienced problems with some slower optos even
> though it was "in spec." I'd allow a healthy
> margin for opto speed if it is a known problem.

Only speaking from personal experience. When I started fiddling with MIDI 15
or so years ago, the primary opto specified was the PC900. After reading
Hal Chamberlin's "Musical Applications for Microprocessors" I've had good luck
using the HP 6N138 and 6N139 Darlingtons. Never a problem and always easily
accessible.

BAJ

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2003\02\27@110322 by fred jones

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You are right.  The Sharp PC900 was almost imposible to get.  I used the
6N138 with no problems also.  Back then optos were slow but today you can
get much faster ones with no problems I'll bet.
FJ






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2003\02\27@120659 by William Chops Westfield
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>  Back then optos were slow but today you can
>  get much faster ones with no problems I'll bet.

A little.  Like 40Gbps sonnet transceivers with a bit of fiber?

:-)
BillW

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2003\02\27@201106 by Mike Morris

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At 12:40 AM 2/27/2003 -0800, Neil Bradley wrote:
>For those interested, the MIDI baud rate was selected because of its ease
>of implementation in the CPU used in the original Sequential Circuits
>Prophet 600.

Actually, I believe the baud rate selection was based on the fastest opto
commonly available at the time. If anyone *really* cares, I'll ask a friend
who worked for Sequential. As far as current optos, the 6N138 works perfectly.

- Mike

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