6502.org

Hello 10 all,

In this thread: 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 connected the RD logic direct with other gates or RAM, see image bottom. I'm calling it Min(n)i(e) Mouse Logic.

In my Atom I used it with 74LS×× logic, µp clock at 1MHz and all diodes 1N4148, but I'm not sure if it will also work at higher frequencies, 100K resistor and 74HC(T) families.

Please comment !

(Mouse images from Wikipedia)

Hi, Louis! I do like that address selector.

The 4 to 1 decoder is neat, and I 98% get it. The diode and the 10K resistor confuse me slightly. I think the diode is part of a wired OR gate to push the 1B output high in some cases. The 10K is a pull up, but I'm not sure why it's needed.

Hi Martin,
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 that the signals are running from right to left (hence the diode pointing in the other direction).

The diode and resistor form an AND gate that provides an extra input to the 2-input NAND that produces the signal for the /0 output. Thus the outputs of /3, /2 and /1 are the inputs of a 3-input NAND gate generating output /0, according to negative logic: if non of /3, /2, /1 is active (low), /0 must be active (low).

Back then (half a century ago) I had no 1 of 4 selector, what I did have was a whole tube full of 74LS00 (quad 2-input NAND ICs) and a bunch of 1N4148 and 10K, so I soldered this Mini Mouse Tail onto a 74LS00.

Hello NTS,
Thank you

I have a good supply of 74HC00s, as I'm pretty sure most people here do. It stands to reason that I'll find a few 1N4048s in my assortment as well.

Hello NTS,

I had to correct this: the diodes are 1N4148.
(I even doubt whether a 1N4048 exists.)

So I've led you astray. Sorry about that.

For more information on the 1N4148, see: https://en.wikipedia.org/wiki/1N4148_signal_diode

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 specific info at: https://en.wikipedia.org/wiki/1N58xx_Schottky_diodes

After staring at the address decoder, running though all four combinations, I get it now.

Oh. I found 100 of those whilst digging in my parts boxes this evening.