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Classic Display Notes
06-30-2019, 10:35 AM (This post was last modified: 06-30-2019 10:38 AM by teenix.)
Post: #1
Classic Display Notes
Hi all,

I posted a PDF file with some Classic display notes I threw together if anyone is interested.

They are not as comprehensive as Jarques Laporte's excellent works but may be useful just the same.

http://www.teenix.org/ClassicDisplay.pdf

cheers

Tony
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06-30-2019, 02:53 PM
Post: #2
RE: Classic Display Notes
Tony:

As always, great work! Thank you again for your excellent engineering preservation activities!

TomC
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07-01-2019, 01:17 AM
Post: #3
RE: Classic Display Notes
Hi all,

Caution: Techy stuff follows :-)

Has anyone figured out how the Classic cathode driver is actually stepped to the next digit? I've looked around and no info. I know it's just a simple pulse, but how that pulse is generated is confusing.

I know there are errors shown on the HP45 patent document. One in particular (I think) is the RCD line that resets the cathode driver scan. My scope sees the pulse as 20uS during T4, whereas the HP diagram (Fig 18) shows a 1.25 uS pulse on T1.

The C CL pulse is supposed to step the cathode driver to the next display digit on its rising pulse edge and is shown doing this in Fig 18. It occurs just as the first LED segment of the digit is about to be excited (segment E).

I'm not sure how this works as it suggests that after a scan reset, the first digit is stepped over before it gets displayed. This obviously doesn't happen so I'm a bit confused.

This pulse is also tied to the anode driver [E] line from the ARC chip which seems to suggest that the LED G segment being lit or not affects the stepping also, which to me doesn't make sense.

PS Not expecting an answer, but you never know :-)

cheers

Tony
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07-03-2019, 06:31 AM
Post: #4
RE: Classic Display Notes
Hi all,

Doing a heap of research for the Classic displays paid off.

What's even more cool, the whole circuit based on a PICmicro is running off a 3.7V supply.

:-)

cheers

Tony


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07-03-2019, 08:39 AM
Post: #5
RE: Classic Display Notes
(07-03-2019 06:31 AM)teenix Wrote:  Hi all,

Doing a heap of research for the Classic displays paid off.

What's even more cool, the whole circuit based on a PICmicro is running off a 3.7V supply.

:-)

cheers

Tony

Wow! How did you do that?
I did not see a chance of getting it to work without the DMA. Thats why I went for the renesas controller.

Cheers,
Harald
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07-03-2019, 10:16 AM
Post: #6
RE: Classic Display Notes
(07-03-2019 08:39 AM)Harald Wrote:  Wow! How did you do that?
I did not see a chance of getting it to work without the DMA. Thats why I went for the renesas controller.

Cheers,
Harald

It was a bit of a surprise to me also. Except for the power supply everything is bread boarded with flying leads. It was squinty eyes and a nervous finger on the power switch Smile

The PIC can collect and output the Anode data in 375nS plus a small time needed to detect when to do it. I suspect the inductor charge time is eaten into a little bit but the display seems bright enough.

I am yet to hook up the scope to see what it happening on the inductors. Even though the LEDs light up ok, it might be doing it just barely, but I think I have another trick up my sleeve to all but eliminate the latency.

cheers

Tony
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07-03-2019, 06:30 PM (This post was last modified: 07-03-2019 07:21 PM by Harald.)
Post: #7
RE: Classic Display Notes
(07-03-2019 10:16 AM)teenix Wrote:  
(07-03-2019 08:39 AM)Harald Wrote:  Wow! How did you do that?
I did not see a chance of getting it to work without the DMA. Thats why I went for the renesas controller.

Cheers,
Harald

It was a bit of a surprise to me also. Except for the power supply everything is bread boarded with flying leads. It was squinty eyes and a nervous finger on the power switch Smile

The PIC can collect and output the Anode data in 375nS plus a small time needed to detect when to do it. I suspect the inductor charge time is eaten into a little bit but the display seems bright enough.

I am yet to hook up the scope to see what it happening on the inductors. Even though the LEDs light up ok, it might be doing it just barely, but I think I have another trick up my sleeve to all but eliminate the latency.

cheers

Tony

Hi Tony,

I am very keen to see your design.

You have to be careful not to charge the inductors without any of the cathode transistor turned on. That will result in an overvoltage that will sooner or later destroy the anode drive. I have solved this by soldering a green LED across one of the cathode transistors. That dissipates the energy and saves the anode driver. Also it indicates if you still have any glitches (I did at startup) that cause problems. The original HP hardware has a startup problem too, but only a very short pulse occures.

Cheers,
Harald

Edit:
To avoid misunderstandings, the green LED was only a temporary measure during development. Once I was satisfied it never turned on anymore I removed it.
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07-07-2019, 03:13 AM (This post was last modified: 07-07-2019 03:14 AM by teenix.)
Post: #8
RE: Classic Display Notes
Hi all,

I managed to get a nice shot of the step pulses from the anode driver plus the extra one when the decimal point is displayed. The display is showing 0.00

I've updated the classic display notes to suit.

http://www.teenix.org/ClassicDisplay.pdf

cheers

Tony


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07-09-2019, 07:18 PM
Post: #9
RE: Classic Display Notes
(07-01-2019 01:17 AM)teenix Wrote:  Hi all,

Caution: Techy stuff follows :-)

Has anyone figured out how the Classic cathode driver is actually stepped to the next digit? I've looked around and no info. I know it's just a simple pulse, but how that pulse is generated is confusing.

I know there are errors shown on the HP45 patent document. One in particular (I think) is the RCD line that resets the cathode driver scan. My scope sees the pulse as 20uS during T4, whereas the HP diagram (Fig 18) shows a 1.25 uS pulse on T1.

The C CL pulse is supposed to step the cathode driver to the next display digit on its rising pulse edge and is shown doing this in Fig 18. It occurs just as the first LED segment of the digit is about to be excited (segment E).

I'm not sure how this works as it suggests that after a scan reset, the first digit is stepped over before it gets displayed. This obviously doesn't happen so I'm a bit confused.

This pulse is also tied to the anode driver [E] line from the ARC chip which seems to suggest that the LED G segment being lit or not affects the stepping also, which to me doesn't make sense.

PS Not expecting an answer, but you never know :-)

cheers

Tony

Hi Tony,

This is how I think it works:

The data to be displayed is controlled by the ARC (Arithmetic and Register Circuit).

The ARC has to synchronize the anode driver and cathode driver for displaying of the data in the correct way.

To synchronize the anode driver with the ARC, the anode driver resets itself if input B and D are high and Phi1 is low.
This is an internal reset signal, not accessible from the outside. This pulse is shown in Fig 18.
In this way the ARC knows (forces) the T state of the anode driver.

To synchronize the cathode driver with the ARC, the ARC generates the RCD (Reset Cathode Driver ?) pulse.
This pulse is indeed 5 us long and appears during T4.

The cathode driver gets the C CL pulse from the anode driver to step to the next digit.
(This signal could also be generated by the ARC, but this solution is more simple, I think).
Best regards,

Kees
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07-09-2019, 11:16 PM (This post was last modified: 07-09-2019 11:16 PM by teenix.)
Post: #10
RE: Classic Display Notes
Hi Kees,

Many thanks for the reply. I agree, in that I suspect a few extra gates in the anode driver creates a simpler system overall.

cheers

Tony

(07-09-2019 07:18 PM)Kees van der Sanden Wrote:  Hi Tony,

This is how I think it works:

The data to be displayed is controlled by the ARC (Arithmetic and Register Circuit).

The ARC has to synchronize the anode driver and cathode driver for displaying of the data in the correct way.

To synchronize the anode driver with the ARC, the anode driver resets itself if input B and D are high and Phi1 is low.
This is an internal reset signal, not accessible from the outside. This pulse is shown in Fig 18.
In this way the ARC knows (forces) the T state of the anode driver.

To synchronize the cathode driver with the ARC, the ARC generates the RCD (Reset Cathode Driver ?) pulse.
This pulse is indeed 5 us long and appears during T4.

The cathode driver gets the C CL pulse from the anode driver to step to the next digit.
(This signal could also be generated by the ARC, but this solution is more simple, I think).
Best regards,

Kees
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