RTL Logic

[Steve Thatcher]

actually you can wire-or with diodes as long as you pay attention to the "higher" low logic level. Naturally, the voltage is not TTL compatible, but I have used that technique also. As for totem pole vs open collector, that is why I mentioned reading the specs rather than getting more technical with output types. I don't think anyone is going to whip out their TTL chips and start connecting them up to see which one works and which one doesn't.

-----Original Message-----
From: Scott Stevens <chenmel at earthlink.net>
Sent: Jan 7, 2005 10:33 PM
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
Subject: Re: RTL Logic

On Fri, 7 Jan 2005 12:59:57 -0800 (PST)
Tom Jennings <tomj at wps.com> wrote:

> On Fri, 7 Jan 2005, Steve Thatcher wrote:
> 
> > dirt has been known to be found in most places in the world...
> >
> > doing a wired-or and wired-and depends on reading IC specifications
> > for specific chips. It is what design engineers do...
> 
> Sorry for being so obtuse! Phrase meant: "wire OR/etc was very
> common in RTL".
> 
> I tried wired-OR once in TTL, didn't like the results :-)
> 

Wired-OR will work fine for open-collector output TTL.  It will fail
miserably with totem-pole output parts.  A 'battle of the transistors'
will ensue and one output or another will win.