Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!lzaz!hcj
From: hcj@lzaz.ATT.COM (HC Johnson)
Newsgroups: comp.sys.atari.st
Subject: Re: NEC P2200 compatibility
Summary: you are both right
Message-ID: <626@lzaz.ATT.COM>
Date: 13 Jun 89 14:33:49 GMT
References: <890612-090337-12728@Xerox>
Organization: AT&T ISL Lincroft NJ USA
Lines: 46

In article <890612-090337-12728@Xerox>, "chaz_heritage.WGC1RX"@XEROX.COM writes:
> In his Thu, 1 Jun 89 14:56 N Roger Hunen writes:
> 
> >If you have a NEC P2200 connected to your ST *without* modifica-
>      tion, DISCONNECT it now.The 1 kOhm pull-up resistors on the Cen-
>      tronics interface of the NEC will eventually kill the sound chip
>      of your ST.<
> 
> Has anyone out there actually had their ST damaged by using it with a
> P2200? Until Mr. Hunen posted his fix for the problem I didn't know it
> existed - I had to call NEC (UK) to get some driver software for my ST to
> dump Degas correctly on my new P2200, and they didn't mention any hardware
> compatibility problem at that time.
> 
> I'd like to use a printer buffer on my system, to allow me to keep on
> working while printing Degas or CAD frames, which take forever. Would such
> a buffer provide the correct pull-ups? Or would it also be likely to damage
> the ST? Has anyone tried it? I don't really want to make up Mr. Hunen's fix
> box only to make it redundant afterwards by buying a printer buffer.
> 
> Anyone got any clues?

What is being overlooked is that the specs on chips are 'guaranteed' minimums.
Thus while the sound chip guarantees to sink 1.6 ma, it doen not mean that
it wont do better than that.

Also, from the various specs posted, it would appear that not all lines may
have 1000 ohm pull ups on different devices.  If only a couple (control)
lines need 5 ma, it may not be noticed.

Also, as was previously pointed out, the first order effect of a 1000 ohm
pullup is that the ON signal will not pull to 0.3 volts, but instead to a
higher level, which may or may not be interpreted correctly.  Marginal
performance would be the likely result.

It is more likely that a 1000 ohm device will fail to work before it could
damage the ST.

On Bus repeaters and electronic printer switches:
If they have 1000 ohm terminators, same problem.  The one I have works
on long leads so I'd say its designed to use lower currents.

Howard C. Johnson
ATT Bell Labs
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hcj@lzaz.att.com