Alt-BEAM Archive
Message #02063
To: beam@corp.sgi.com, hannah@nanospace.com, David@quidan.demon.co.uk
From: Don Day DON@rgb.com
Date: Tue, 06 Apr 1999 16:24:17 -0700
Subject: [alt-beam] Re: Bicore using 74xx240 -Reply
74LS parts are difficult for this.
Their input currents are asymmetrical
50ua Ih, -400ua Il
and also fairly high.
The input currents will will overwhelm the
currents through high value resistors.
The only way to get longer time constants is with
larger capacitors, probably electrolytics, which
may well have leakage problems of their own.
The 74LS output currents are also asymmetric,
tested at 3ma Oh, 24ma Ol,
And the being TTL the threshold is asymmetric,
at 1.4V not 2.5V,
and the power supply range is narrower, 4.5V-5.5V.
The CMOS families 74C, 74HC, 74AC,
make everything much easier.
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