HP-65 1333A02242 display missing all the decimal dots

[teenix]

(11-09-2020 01:32 PM)albertofenini Wrote:  Thanks Tony,
I understand that I'm missing some basic knowledge, and I should go back to study the documents ...
What is the purpose of each of disp0, disp1, disp2, disp3, disp4 ?
Is disp4 wat you call "step" ?
I know that it may be not easy to summarize these concepts so I will appreciate
any hints that will help to better understand the working scheme ...
For instance, with reference to the PDF you mentioned at the beginning of this post
can we say Disp0 = A, Disp1 = B, Disp2 = C, Disp3 = D, Disp 4 = E ?

Hi Alberto,

The display for the Classics looks simple but is quite a complex setup. The Classic Notes PDF document link that I provided earlier explains how it all works with images from my oscilloscope and there is more information available in the HP-45 patent document which is available on the web or I can email if you like.

Re: Disp0=A etc., yes, that is correct.

In simple terms, the 5 lines have partially decoded display information on them and is fed to the anode driver which fully decodes that into 7 segment display control.

This data (very quickly - in 20uS time slots) charges and discharges the coils to turn on the appropriate LEDs for each digit.

After all 8 LED segments are either turned on or off depending on the digit to display, the "step" signal from the anode driver tells the cathode driver to move to the next digit and the anode information (lines 1-5) continues.

However, before the "step" occurs, if there is a decimal point to display (segment H) then the anode drives issues an extra "step" signal and the next digit shows a decimal point only. This functionality is explained and shown in diagrams in both the mentioned PDF files.

Happy to help further if I can :-)

cheers

Tony