If you experience any problems, due to the forward voltage drop of the 1N4148 (which can be to high for some logic families), try Schottky diodes, they have a lower forward voltage drop.

For a little explanation of those, have a look at: https://en.wikipedia.org/wiki/Schottky_diode
and more ...

Hello NTS,

... what I did have was a whole tube full of 74LS00 (quad 2-input NAND ICs) and a bunch of 1N4048 and 10K....
I had to correct this: the diodes are 1N4148. :mrgreen:
(I even doubt whether a 1N4048 exists.)

So I've led you astray.
It stands to reason that I'll find a few 1N4048s in ...

Hello NTS,
Thank you

Hi Martin,

The 4 to 1 decoder is neat, and I 98% get it. The diode and the 10K resistor confuse me slightly.
I understand the diagram is a bit confusing, look at it this way, that diode and resistor have the same function as in the n-input NAND gate Mickey is pointing at, the only difference is ...

Hello 01 all,

For (possibly) even smaller logic than M²L, check out Min(n)i(e) Mouse Logic
viewtopic.php?f=4&t=8553

Hello 10 all,

In this thread: http://forum.6502.org/viewtopic.php?f=4&t=8544 , I saw the well known Mickey Mouse Logic.

I think it could still be a tiny bit smaller. Using the pull-up/pull-down resistors for an input, in my old Atom I even ommited the Inverter/Follower Schmitt trigger and ...

Hi Neil,
I tried it too and it was indeed a slow connection and difficult to download at the moment (suppose location/time dependant).
I already downloaded that file some time ago, maybe this will help:

Duke Nukem says "Typos happen".

Hello Gart, Ah, jea, I'm "a bit" dyslexic, didn't notice there was missing an F.

Thanks

Hello Dave,
I was interested, tried to download the 6512 datasheet.
To my surprise, the link returned a "404 Not Found".

That’s the trouble with starting a new topic about the same thing. :D The continuity goes out the window and old codgers such as moi lose track of things. Perhaps this is why every time I see the doctor she asks me about my cognitive abilities. :shock:
Maybe a simple Solution could help:
The ...

Hello 0010 all,


With the above circuit, if RAM is selected during Ø2 low, there will be only one gate delay after Ø2 goes high before /RD or /WD is asserted. Using 74AC or 74AHC logic, that delay will be in the single-digit nanosecond range.

If you don't want to spend ¾ 74xx00 on it, but have ½ ...

Hello ttlworks,

• AN-0815_Color_Graphics_For_The_MC68000_Using_The_MC6847.pdf
• How did the Dragon modify 6847 video output timing for PAL?
Thanks for the links ❗

I already knew about bitsavers, but the web can be quite a haystack when one is looking for an odd needle like this.

You guessed ...

Hello to all,

In the Acorn Atom, the MC6847 CRTC (VDG) is fed with only eight bits of data, but to do full justice to the MC6847 four extra bits might be used for the mode control lines INT/EXT, INV, A/S and CSS , which than can be changed on character-by-character basis.

The pin numbers and ...

Hello BDD,

As previously noted, . . .

Thanks for the crystal-clear explanation ❗
(Sorry, for me making you repeating things.)

The summarisation you wrote in answer to my questions, is much more comprehensible than all those different timing diagrams from all those different manufacturers; it ...