# encoder simplification

#### Schoen85

Joined Jul 30, 2013
3
Greatings,

I was trying to get the simplified exapressions on this page. However I did not get the same result for D0. im new at this so maybe I am wrong.

#### tshuck

Joined Oct 18, 2012
3,534
Without going too much in depth at the moment, the labels on your seven segment display is different, so coming up with a different result is expected. Whether or not yours is correct is another thing...

#### Georacer

Joined Nov 25, 2009
5,182
You seem to have a point.

On the Boolean function for D0, there is the I1 term which forces row 7 to be 1, instead of the desired 0.

I 'd like another one to confirm this before mounting it in the corrections list.

#### tshuck

Joined Oct 18, 2012
3,534
yeah, just look at the row for 4. I'm not sure what character would be displayed, but it certainly wouldn't be 4... and the 3 is backwards...

#### Georacer

Joined Nov 25, 2009
5,182
I found another culprit. The numbering of the segments in the e-book is wrong. Your D0 is at the bottom of the figure, whereas in the e-book it's on the top.
Schoen, based on the truth table, your notation is correct.

But on top of that, there is the error of the Boolean function extraction that you pointed out.

We need to re-calculate the Boolean functions.

#### Schoen85

Joined Jul 30, 2013
3
I noticed from a previous page that if you rearrange the 7 Seg display so that D0 is on bottom and D6 is on top then the truth table is correct. But if the table is correct the simplification isn't.

#### Dcrunkilton

Joined Jul 31, 2004
422
I find if I re-arrange the LED figure, the table matches.

------6------
| .......... |
5 .........4
| ...........|
------3------
|........... |
2..........1
| ...........|
------0------

However, as you point out, the equations, logic diagram, and PLC diagram don't match.
This should keep me busy for a day or two.

And, Schoen85 gets the prize for the all-time worst error I have ever seen since Tony Kuphaldt passed the baton. How many years has that been. Meaning there is no way possible to blame him for this one. This one was entered on my watch. Once I get the corrections entered I will need you guys to review it in detail. That is how extensive the re-work will be.

Dennis

Last edited:

#### tshuck

Joined Oct 18, 2012
3,534
[...]Once I get the corrections entered I will need you guys to review it in detail.[...]
You've got it.

Thanks for doing all this., I'll help where I can.

#### Dcrunkilton

Joined Jul 31, 2004
422
Now that I have The 7-segment decoder revised, I need your help in checking if for errors, which I should have done when the original author donated it. After renumbering the LED image, I found that renumbering the equations for LED outputs D6, D5, D4, ... to D0, D1, D2 yielded almost correct equations. I also made some additional simplifications. This is shown in the new K-map images.

Here is a link to the revised text and images at ibiblio.org :
http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_9.html#xtocid101564

The gate diagram for the 7-segment decoder has the equations listed near the outputs which should aid in checking for errors (once you agree the equations are correct).

http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/04464.png

Once we agree that the gate diagram it is error free, we have the option of removing the equations so that the diagram image can be wider. I am looking for input on that.

Since the equations changed, the correspond relay ladder logic also changed. Another item needing verification. Ladder logic:

http://www.ibiblio.org/kuphaldt/electricCircuits/Digital/04483.png

This is a list of files and images changed at ibiblio in the Digital directory. This may be of value in a partial update of images at AAC. * = .png for AAC
contrib.sml combin.sml 14169.* 14174.* 14175.* 14176.* 14171.* 04464.* 04483.* 04489.* 04487.*