Forums

Need to construct the logical reverse of a 7448 - perhaps using a GAL

Started by John Robertson October 8, 2018
I am looking for a way to take the TTL level outputs (treating them as 
inputs) of a 7448 and convert them back to the original BCD TTL input 
levels (but as outputs) and I figured a simple socketed GAL would do the 
trick for the least cost. However I don't have the skill set to build 
the GAL logic table for this. Any suggestions? And no, I can't simply 
remove the 7448 from the circuit.

Go easy on me here, I can unscrew hardware, but Boolean has never been 
my forte...

Thanks!

John :-#)#
-- 
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
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                      www.flippers.com
        "Old pinballers never die, they just flip out."
On Mon, 8 Oct 2018 17:20:35 -0700, John Robertson <spam@flippers.com>
wrote:

>I am looking for a way to take the TTL level outputs (treating them as >inputs) of a 7448 and convert them back to the original BCD TTL input >levels (but as outputs) and I figured a simple socketed GAL would do the >trick for the least cost. However I don't have the skill set to build >the GAL logic table for this. Any suggestions? And no, I can't simply >remove the 7448 from the circuit. > >Go easy on me here, I can unscrew hardware, but Boolean has never been >my forte...
Ok, a 7 segment display to BCD converter. <http://slidegur.com/doc/1081821/7-segment-to-bcd-converter> The truth table on Pg 5, logic on Pg 6, and schematic on Pg 8 should be sufficient to produce a PLA or SSI implementation. So, do I get a finders fee? -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On 2018/10/08 6:57 PM, Jeff Liebermann wrote:
> On Mon, 8 Oct 2018 17:20:35 -0700, John Robertson <spam@flippers.com> > wrote: > >> I am looking for a way to take the TTL level outputs (treating them as >> inputs) of a 7448 and convert them back to the original BCD TTL input >> levels (but as outputs) and I figured a simple socketed GAL would do the >> trick for the least cost. However I don't have the skill set to build >> the GAL logic table for this. Any suggestions? And no, I can't simply >> remove the 7448 from the circuit. >> >> Go easy on me here, I can unscrew hardware, but Boolean has never been >> my forte... > > Ok, a 7 segment display to BCD converter. > <http://slidegur.com/doc/1081821/7-segment-to-bcd-converter> > The truth table on Pg 5, logic on Pg 6, and schematic on Pg 8 should > be sufficient to produce a PLA or SSI implementation. > > So, do I get a finders fee? >
That was fast, Jeff! Did you whip that up just now? I am impressed. Dinner on me next time you are in Vancouver, BC! Or a donation to your favourite charity perhaps? John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."
On 2018/10/08 6:57 PM, Jeff Liebermann wrote:
> On Mon, 8 Oct 2018 17:20:35 -0700, John Robertson <spam@flippers.com> > wrote: > >> I am looking for a way to take the TTL level outputs (treating them as >> inputs) of a 7448 and convert them back to the original BCD TTL input >> levels (but as outputs) and I figured a simple socketed GAL would do the >> trick for the least cost. However I don't have the skill set to build >> the GAL logic table for this. Any suggestions? And no, I can't simply >> remove the 7448 from the circuit. >> >> Go easy on me here, I can unscrew hardware, but Boolean has never been >> my forte... > > Ok, a 7 segment display to BCD converter. > <http://slidegur.com/doc/1081821/7-segment-to-bcd-converter> > The truth table on Pg 5, logic on Pg 6, and schematic on Pg 8 should > be sufficient to produce a PLA or SSI implementation. > > So, do I get a finders fee? >
Opps, I did not define the parameters correctly - it is the full 7448 table, minus the Lamp Test that is needed 0 - 15. I think I can figure the extra alpha characters from what you have provided. Thanks again, John :-#)#
On 2018/10/08 7:13 PM, John Robertson wrote:
> On 2018/10/08 6:57 PM, Jeff Liebermann wrote: >> On Mon, 8 Oct 2018 17:20:35 -0700, John Robertson <spam@flippers.com> >> wrote: >> >>> I am looking for a way to take the TTL level outputs (treating them as >>> inputs) of a 7448 and convert them back to the original BCD TTL input >>> levels (but as outputs) and I figured a simple socketed GAL would do the >>> trick for the least cost. However I don't have the skill set to build >>> the GAL logic table for this. Any suggestions? And no, I can't simply >>> remove the 7448 from the circuit. >>> >>> Go easy on me here, I can unscrew hardware, but Boolean has never been >>> my forte... >> >> Ok, a 7 segment display to BCD converter. >> <http://slidegur.com/doc/1081821/7-segment-to-bcd-converter> >> The truth table on Pg 5, logic on Pg 6, and schematic on Pg 8 should >> be sufficient to produce a PLA or SSI implementation. >> >> So, do I get a finders fee? >> > > Opps, I did not define the parameters correctly - it is the full 7448 > table, minus the Lamp Test that is needed 0 - 15. I think I can figure > the extra alpha characters from what you have provided. > > Thanks again, > > John :-#)#
And I see now that this was built by three other guys: Imran Khan, Jabbar Khan, and Kaved Iqbal. Perhaps some thought exercise? The tables show up in a few places, but haven't found the original and the bottom of the schematic appears to be clipped. Still it gives me enough to work with and I can fill in the rest. Mostly it is getting the correct place to start that screws me up... Jeff, I'll still buy you a dinner if you get up to Vancouver, BC area! John :-#)#
On Monday, October 8, 2018 at 9:57:49 PM UTC-4, Jeff Liebermann wrote:
> On Mon, 8 Oct 2018 17:20:35 -0700, John Robertson <spam@flippers.com> > wrote: > > >I am looking for a way to take the TTL level outputs (treating them as > >inputs) of a 7448 and convert them back to the original BCD TTL input > >levels (but as outputs) and I figured a simple socketed GAL would do the > >trick for the least cost. However I don't have the skill set to build > >the GAL logic table for this. Any suggestions? And no, I can't simply > >remove the 7448 from the circuit. > > > >Go easy on me here, I can unscrew hardware, but Boolean has never been > >my forte... > > Ok, a 7 segment display to BCD converter. > <http://slidegur.com/doc/1081821/7-segment-to-bcd-converter> > The truth table on Pg 5, logic on Pg 6, and schematic on Pg 8 should > be sufficient to produce a PLA or SSI implementation. > > So, do I get a finders fee?
This logic diagram is not optimal. I guess a Karnaugh map for 7 inputs is not so easy to draw. I was thinking about this recently. When I was in school they taught Karnaugh maps because you would use them from time to time. Later they taught Karnaugh maps because you needed to know how they worked so you could potentially write your own minimization programs I suppose. I expect they barely teach Karnaugh maps because there is tons of software around to do this for you much as they don't emphasize simple arithmetic when you will likely use a calculator. I think this is a lot simpler to construct from SSI than the diagram shown. Or maybe a very few MSI devices could be used. Or mux logic (which I was taught in school) could be used much as is done in FPGAs. I haven't checked, but I bet this could be done with maybe six devices. Rick C.
On Mon, 8 Oct 2018 19:27:04 -0700, John Robertson <spam@flippers.com>
wrote:

>And I see now that this was built by three other guys: Imran Khan, >Jabbar Khan, and Kaved Iqbal. Perhaps some thought exercise? The tables >show up in a few places, but haven't found the original and the bottom >of the schematic appears to be clipped.
Switch to full screen view and the bottom of the tables and schematics will magically appear. I think the original was a powerpoint presentation, but I didn't bother trying to find it. I'll do some digging and post what I find after I extract all the wood splinters from my hands. Searching for the 3 authors names, or an image search by one of the graphics pages should work.
>Still it gives me enough to work with and I can fill in the rest. Mostly >it is getting the correct place to start that screws me up... > >Jeff, I'll still buy you a dinner if you get up to Vancouver, BC area!
Probably not, but I do have some friends along the way I wouldn't mind visiting. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"John Robertson" <spam@flippers.com> wrote in message 
news:FpWdnYuq0ujJaSbGnZ2dnUU7-I_NnZ2d@giganews.com...
>I am looking for a way to take the TTL level outputs (treating them as >inputs) of a 7448 and convert them back to the original BCD TTL input >levels (but as outputs) and I figured a simple socketed GAL would do the >trick for the least cost. However I don't have the skill set to build the >GAL logic table for this. Any suggestions? And no, I can't simply remove >the 7448 from the circuit. > > Go easy on me here, I can unscrew hardware, but Boolean has never been my > forte... > > Thanks! > > John :-#)# > --
One way to do it is to use an EPROM. Connect the seven segments to AD0 to AD6. Use the first four data outputs (D0 to D3) for the BCD code. Make up a table with the correct memory locations to put 1s in for the decoder. Tie /CE and /CS to the appropriate levels. A 2716 would work fine, just ignore the unwanted outputs and tie AD7 to ground. Regards
On 2018/10/08 8:27 PM, gnuarm.deletethisbit@gmail.com wrote:
> On Monday, October 8, 2018 at 9:57:49 PM UTC-4, Jeff Liebermann wrote: >> On Mon, 8 Oct 2018 17:20:35 -0700, John Robertson <spam@flippers.com> >> wrote: >> >>> I am looking for a way to take the TTL level outputs (treating them as >>> inputs) of a 7448 and convert them back to the original BCD TTL input >>> levels (but as outputs) and I figured a simple socketed GAL would do the >>> trick for the least cost. However I don't have the skill set to build >>> the GAL logic table for this. Any suggestions? And no, I can't simply >>> remove the 7448 from the circuit. >>> >>> Go easy on me here, I can unscrew hardware, but Boolean has never been >>> my forte... >> >> Ok, a 7 segment display to BCD converter. >> <http://slidegur.com/doc/1081821/7-segment-to-bcd-converter> >> The truth table on Pg 5, logic on Pg 6, and schematic on Pg 8 should >> be sufficient to produce a PLA or SSI implementation. >> >> So, do I get a finders fee? > > This logic diagram is not optimal. I guess a Karnaugh map for 7 inputs is not so easy to draw. I was thinking about this recently. When I was in school they taught Karnaugh maps because you would use them from time to time. Later they taught Karnaugh maps because you needed to know how they worked so you could potentially write your own minimization programs I suppose. I expect they barely teach Karnaugh maps because there is tons of software around to do this for you much as they don't emphasize simple arithmetic when you will likely use a calculator. > > I think this is a lot simpler to construct from SSI than the diagram shown. Or maybe a very few MSI devices could be used. Or mux logic (which I was taught in school) could be used much as is done in FPGAs. I haven't checked, but I bet this could be done with maybe six devices. > > Rick C. >
My thought was to trick a GAL into being essentially a ROM lookup table. should be enough gates inside for that. Using the link Jeff provided I have adapted the boolean equations that I am hoping can be further simplified, (f' = NOT-f), but I am done for now: W = abcdfg + bcdef&rsquo;g + a&rsquo;b&rsquo;cdefg + a&rsquo;b&rsquo;c&rsquo;def&rsquo;g&rsquo; + abc&rsquo;defg + ab&rsquo;c&rsquo;d&rsquo;efg X = ab&rsquo;cdfg+ a&rsquo;bcd&rsquo;e&rsquo;fg+ abcd&rsquo;e&rsquo;f&rsquo;g&rsquo; + a&rsquo;b&rsquo;c&rsquo;def&rsquo;g&rsquo; + a&rsquo;bcdef&rsquo;g + abc&rsquo;defg + ab&rsquo;c&rsquo;d&rsquo;efg Y = abc&rsquo;deg + abcdf&rsquo;g + ab&rsquo;cdefg + abcd&rsquo;e&rsquo;f&rsquo;g&rsquo; + abcdef&rsquo;g + a&rsquo;b&rsquo;cdefg + ab&rsquo;c&rsquo;d&rsquo;efg Z = bcd&rsquo;e&rsquo;f&rsquo;g&rsquo;+ abcde&rsquo;g+ ab&rsquo;cde&rsquo;fg + a&rsquo;b&rsquo;cdefg + a&rsquo;bcdef&rsquo;g + ab&rsquo;c&rsquo;d&rsquo;efg Truth table can't display it here, so I put it here: ftp://flippers.com//usr/www/users/flip/images/temp/7-segment-to-BCD-truth-table.png John :-#)#
On Mon, 08 Oct 2018 21:06:13 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>I think the original was a powerpoint presentation, but I didn't >bother trying to find it. I'll do some digging and post what I find >after I extract all the wood splinters from my hands.
Here's the original PPT presentation: <https://www.slideserve.com/tasha-bullock/7-segment-to-bcd-converter> You can download the presentation as JPG's. Scroll down to "Presentation Transcript". Click on the titles of each page that are to the right of the thumbnail image. You should get a JPG of each page. Back to pulling splinters (don't ask what I did wrong this time). The schematic does look like the bottom is cut off, but it's not. Those 7 lines are the 7 input lines drawn as a bus. There's nothing connected to them below the bottom of the page where they end. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558