I just noticed the 74LS49 BCD-to-7-segment driver makes 6 and 9 without top and bottom horizontals, respectively. The 54LS49 and every 7-segment LED/LCD device I checked make 6 and 9 with top and bottom horizontals. Is there a story here? Does anyone have a common device that makes 6 and 9 the "old" way without the horizontals? It might be a collectors item. Or not. (:-)
Example:
***
-- According to my 1988 TI TTL Logic data book, the \'6\' and the \'9\' tails are missing for both the 54 and 74LS49, as well as the 54 and 74LS47 and 48, and the 54 and 7446, 47A, and 48.
According to my 1976 "Mustard Bible" (Second Edition), page 7-23:
"The SN54246/74246 through '249 and the SN54LS247/74LS247 through 'LS249 compose the '6' and '9' with tails and have been designed to offer the designer a choice between two indicator fonts."
-- Keith
That's my recollection. I think the 'tails' started with parts like the 4511, some of which decode all 16 codes.. to distinguish 6 from b you need the tail. Of course with a micro you can do it any way you like.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
This prompted me to want to say, "Of course, with an 82S123, you can do it any way you want...", but when I went to look up an 82S123, I couldn't find one.
What are they using these days for that sort of thing, or do they just embed everything in the flash?
Thanks, Rich
If you are using open collector drivers between the 74LS49 and the LED display, then just add two 7405 inverters. One between input B and segment 'a' and the other between input D and segment 'd'. It was a common fix in the early 1970's.
-- John B
A CPLD will do the trick if you have to have programmable logic, but yeah, normally you'd do the decoding in a little LUT (Look-Up Table) that is essentially free.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
"Rick Nungester" schreef in bericht news: snipped-for-privacy@x40g2000prg.googlegroups.com...
My Texas TTL Data Book (1980) covers the -46 through -49 all without tails. I remember I had an exercise designing the logic also without tails. It was said to require less gates but I never checked. I also remember that some years later someone showed a resistor-diode circuit to add the tails as yet. It was hardly interesting anymore as decoders with tails were commonly available at the time. It did not take very long and displays with fully integrated latch-decoder-driver-leds appeared. I still have some HP
5082-73xx and til311 displays. They may be usefull in some one-of-kind design. Otherwise multiplexed LED-displays or even complete LCD-displays take their place.petrus bitbyter
On Aug 6, 2:38 pm, Spehro Pefhany wrote: > On Mon, 06 Aug 2007 20:05:07 GMT, the renowned Rich Grise >
You can even do this 'trick'. I put this into a clock project that displays day, month and year. It actaully reads pretty well.
GG
I've always used something like:
const unsigned char font[17] = { 0x7e, // 0 0x12, // 1 0xbc, // 2 0xb6, // 3 0xd2, // 4 0xe6, // 5 0xee, // 6 0x32, // 7 0xfe, // 8 0xf2, // 9 0xfa, // a 0xce, // b 0x6c, // c 0x9e, // d 0xec, // e 0xe8, // f 0 // blank };
#define DOT |0x01
Not much extra space used and no extra hardware needed (maybe a shift register to conserve precious I/O pins). I've never found much need for hardware 7 segment display drivers. Then again, I've never encountered a project that i didn't do with at least a microcontroller if not a proper processor.
Sure, I have #defines (or the equivalent) similar to that, but you have to try to avoid words starting with, or containing too many, 'K', 'W', 'X', 'Z' etc.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
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