Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!wuarchive!uunet!mcsun!ukc!slxsys!stevem
From: stevem@specialix.co.uk (Steven Murray)
Newsgroups: sci.electronics
Subject: Re: help! 74ls48 display problem
Message-ID: <1991Mar1.181124.27510@specialix.co.uk>
Date: 1 Mar 91 18:11:24 GMT
References: <9102232331.AA12070@cue.bc.ca>
Organization: Specialix International, London
Lines: 30



On 23 Feb Matt Pratap wrote:

>I have made a 2 digit decimal counter and display using 2 74ls190's
>(up/down decade counter) with 2 74ls48's (7 segment display driver).

>I want the most significant digit (10's) to be blanked when it is
>a '0'.  In theory, all I have to do is ground pin 5 (Blank '0' in)
>of the 7448.  This doesn't seem to work.

I got interested in what you wrote because you were quite specific
about your setup.  I checked Texas Instruments and National Semiconductor
data books, both specify that grounding pin 5 should cause the display
to blank as long as a0-a3 (pins 1,2,6,7) are low - meaning data is 0,
and lamp test is high (pin 3).  They specify that pin 4 will go low in
response to this condition.  I would suggest that you carefully go over
your circuit again, to check if the conditions are actually being met.
As both data books say it works, chances are it does ... actually measure
the voltages on all the pins - preferably with a scope, so you can see
any pulsing.  Good luck.

Regards,
Steven Murray

-- 
Steven Murray
uunet!slxsys!stevem  stevem@specialix.co.uk
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