mpratap@cue.bc.ca (Matt Pratap) (02/24/91)
This may seem like a simple question, but I'm a simple guy :-) 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. Another method I tried was to invert the max/min line from the 74190 and tie it to pin 4 (blank out) of the 7448 (I think this is permissible). This blanks the display on '0' and also '9'. A step closer, but not what I want, since I use '9'. Is there any way to get this accomplished without any more chips? Thanks ------------------------------------------------------------------------- Matt Pratap, Victoria B.C. -=- mpratap@cue.bc.ca * (Insert quote here!) -------------------------------------------------------------------------
stevem@specialix.co.uk (Steven Murray) (03/02/91)
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 I am speaking, but | If these are your opinions, then we are in agreement!! not for my employer.| Flames, spelling errors, complaints > /dev/null