Threaded Mode | Linear Mode

Kees van der Sanden · 07-09-2019, 07:18 PM

(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