8-bitters and multi-whatever

M H Stein dm561 at torfree.net
Thu Sep 13 10:02:04 CDT 2007


------------Original Message:
Date: Wed, 12 Sep 2007 19:56:02 -0400
From: "Roy J. Tellason" <rtellason at verizon.net>
Subject: Re: 8-bitters and multi-whatever

On Wednesday 12 September 2007 19:45, Ensor wrote:
> Hi,
>
>   > You don't even need "rs232 levels".
>
> MIDI is a "current loop" interface isn't it?

Yup!

But my point is that in prototyping some small SBC the rs232 stuff is about 
the only thing on there typically that needs other than logic power (+5V) 
unless there's some analog stuff there on the board that needs it.

MIDI,  in every implementation I've ever seen,  uses only a 5V supply.

I never did understand why current loops weren't used more...

========================
-----------Reply:

On short runs you can usually get away with TTL levels on RS-232 as long 
as you limit the input voltage swing with a resistor and a couple of diodes 
or use an optocoupler.

m




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