[sdiy] MIDI specifications round 2

[Magnus Danielson]

From: "Blitzcraig" <blitz at nmt.edu>
Subject: [sdiy] MIDI specifications round 2
Date: Thu, 17 Apr 2003 13:12:57 -0600 (MDT)

> 
> A lot of helpful info guys, thanks.
> 
> I'm not familiar with UART's, but I'm assuming they're IC's that are used
> for Asynchronous transfer's, add start/stop bit, etc.
> Looking over my microcontroller a little more, I have notice that it has a
> SCI built in.  All I would have to do is set the baud and write to the
> register and it should take care of the start/stop bit for me.  I think I
> should be able to handle the serial stuff from here.

31250 baud, 8 bit, 1 stop bit should most chips be able to handle easilly.
If you don't run any strange crystals it should be a straight forward thing.

> I'm still a bit confused about the pin's, I'm not sure what the current
> loop is/does.  From these schematic/diagrams shown, it looks like my data
> should go through two inverters through a 220ohm resistor?

Two 220 ohm resistors, one from the inverter output and one in the return-path.

> I'm not sure why you would do that other than to delay the data, why?

It's the inverters output characteristics you are after. The delay comes for
free ;O)

> ok, and the other pin is tied high through a 220ohm resistor... this is the
> twisted pair that's mentioned right?

Well, the twisted pair is what the cable should be. The resistors is part of
the cheapertronics diffrential current drive curcuit.

> The middle pin ties to what, I think this is
> confusing because of my lack of current loop knowledge.

Shield/Ground, but this remains something of a discussion somethimes.

Cheers,
Magnus