From: bhunter@hardy.u.washington.edu (Brian Hunter)
Subject: Re: MOTU Apparently Now hiring ex Radio Shack Employees for Tech Support
Followup-To: jonul@microsoft.com
Organization: University of Washington, Seattle
Date: Fri, 10 Apr 1992 15:49:10 GMT

In article <204667@unix.cis.pitt.edu> metlay@minerva.phyast.pitt.edu (metlay) writes:
>A Macintosh apparently cannot send data to a MIDI interface at a throughput
>of greater than 140 kilobaud.
>
>I've turned this problem over and over in my head, taking what little I
>know about Macs (me and the rest of the industry, it seems) and trying 
>to make all the pieces fit. On the one hand, I have many friends who
>use them and swear by them: the same folx John mentioned, like Adam, 
>Nick, Eirikur, et alii. (You know Alii, right?) On the other hand, I
>recalled the last session I did with a Mac, in particular one exchange
>between two people we know and love:
>
>This is how I work. I turn knobs, I run control signals into synths, I 
>generate long, gooey streams of bytes at a very high rate of speed. And
>this apparently is telling me that a Mac can't handle that. Strip away
>all the insults and everything else, and that's what's left: a Mac can't
>use an interface of this type for more than three or four data streams 
>at once without choking. The MTP comes under this aegis, as does every other
>interface out there, including the Studio Plus 5, which HAD been looking
>rather tempting....
>
>Would someone PLEASE point out a verifiable technical spec SOMEWHERE that
>proves me wrong? PLEASE?
>
>--
>metlay  

This message was posted by jonul@microsoft.com, any lines saying that
he is actually bhunter@hardy.u.washington.edu are purely hallucination
on your part.  (enough of this, let's get to the post)

This may be the information you're looking for(taken from the 
Guide to the Macintosh Family Hardware)

The maximum nominal data transmission rate that you can select through
the Macintosh Toolbox is 57,600 baud.  This is the maximum rate that the 
classic Macintosh computers can maintain for transmission of serial data
when the SCC(Serial Coomunications Controller) port is operating
in an asynchronous, interrupt driven fashion, timed by the 3.672 MHz
clock(they refer to the classic Macintosh as the 128, 512, 512KE, and Plus)

Appletalk operates at a nominal data transmission of 230.4 Kbaud.  The
higher rate is possible because AppleTalk Communications are not interrupt
driven; during Appletalk communications, the Appletalk Driver has complete
control of the computer.

The maximum possible tranmission rate for serial data ranges from
approximately 500 Kbaud on the Mac Plus and SE to 900 Kbaud on the
Macintosh II family. To acheive such data transmission rates, the
SCC would have to be operated in synchronous mode timed by an
external clock, and the serial driver would have to have complete
uninterrupted control of the computer.



[end of quote]

So, what they are saying is that if a program follows apples standards
(and uses the toolbox to make serial requests), the max is 57,600 baud.
But if they went direct to the port(which is highly unsupported), that
limit is not there.  I suppose they could right their own serial driver,
but then who's to say that this would be supported under new hardware.

And if they write their own serial drivers, they would be writing their
own MIDI functions, hence getting further and further away from Apple
Standards, and hence risking that it won't work in future software/
hardware. 

But, they could be doing this already(I'm only speculating on what 
routines they use for serial access, but I don't see a hardware 
limitation, just a software limitation that seems to be imposed
by Apple.(Another side note, this may have changed with System 7,
the reference I quote is from a book published in 1990, so the
hardware limitations include machines up to the IIfx, but not the
newer Macs.))

Draw what conclusions you will, but it seems that the ports should
be able to handle this(although I really like the thought of a 
NuBus MIDI card, it makes me smile) %B

Jon

oh yeah, I am technical support for Microsoft, so I guess I'm not supposed
to know this stuff (or even show a remote interest) =)
Newsgroups: rec.music.synth