RS232 in Titan

Thu Apr 24 11:48:28 CEST 1997

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	id sma028679; Thu Apr 24 10:18:42 1997
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Date: Thu, 24 Apr 1997 9:44:12 +0000
To: synthdiy  <synth-diy at horus.sara.nl>
From: Kevin Gale <keving at newcomp.demon.co.uk>
Subject: Re: RS232 in Titan
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     From "Texas Instruments RS-422 and RS-485 Interface Circuits 
     Applications and Data Book":

     "RS-422 and RS-485 are balanced (differential) digital transmission 
     line interfaces..."

     RS-232 is single pole, therefore there is considerable difference 
     between the two.

     Another big difference is the data rate.  RS-232 is specified at a 
     maximum of 20kbaud, whereas RS-422 can achieve in excess of 10 Mbps 
     over twisted-pair cable, hence why Apple use it for their 250kbps 
     AppleTalk bus.

     (bps = bits per second)

     Thirdly, RS-232 is a one-to-one link (TX ------ RX), with data able to 
     flow in both directions.  On the other hand, RS-422 is a one-to-many 
     unidirectional link, e.g. data from a central computer to multiple 
     remote monitors:

        TX ------+----+----+------+
                 |    |    |      |
                RX   RX   RX     RX

     Using RS-422 for MIDI would be possible, since it is effectively 
     similar in principle (one-to-many unidirectional).  Just need to tell 
     the Mac to work at 31.25kbaud.

     Neil Johnson
     ============

>Kevin Gale <keving at newcomp.demon.co.uk> at Internet-PO wrote:
>
>
>

>nope.

>A Mac is definately RS-422. Basically RS-232 without some of the 
>handshaking and modem specific lines.

>Kev.

-------------------------------------- 
Date: 24/04/97 9:18 am
To:  Custodian
From: J.D. McEachin
On Wed, 23 Apr 1997, Paul Schreiber wrote:

> Trivia: How was the MIDI data rate selected? 
> 
> Answer: It was the fastest baud rate an Intel 8751 with a 12Mhz crystal 
could go!!

And guess what's inside the Jupiter6, one of the 1st MIDI synths? A 12Mhz 
8051. (well, actually, 3 of them, and sometimes it's 8031s, but that's 
another story).

> Most PCs today can do 115.2KB all day long, which is 4X MIDI speeds. And 
I don't
> plan IN/OUT/THRU stuff, although somebody else probably will.

So what exactly do you need to transmit across this interface that would 
swamp MIDI?  A MIDI device with a decent serial handler can handle quite 
a bit of MIDI Continuous Controller info w/o bogging down.  It seems that 
the universality of MIDI would outweigh the advantages of 4x bandwidth.  
With MIDI, you could use anything from an MMT8 to Max to access the Titan.

> Is the Apple serial port really RS-422 (which is a differential 
Rs-232)?? Hmmm......

No, it's Rs-232.

JDM