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Yessssss been searching for something like this for years now😭🙏

Mode LHHL . When A >B or A=B then pin G pin 17 os High.

The solution portrayed is not the solution to the underlying problem. :: According to Ben's schematics: /OE of the 28C16's is wired to GND. This is a design fault. Why this has not been addressed yet, despite its obviousness, will likely remain a mystery. It is also a fault that cannot be fixed by patching. Patching only remedies certain bandwidths of clockfrequency, YYMV. :: I don't know if Ben did this on purpose -to teach something- or whether it was an oversight. Or that he, "Just got lucky", as I've seen mentioned elsewhere. (Reading Ben's BIO I cannot but conclude the "teaching" edge, since I'm of the same material.) Nevertheless: - Valid data out of any "memory-unit" is only available while the address is stable within the propagation time. - If the bus is in Hi-Z (i.e. "unknown state") no data is or should be present. NB: Download Ben's schematics (available from eater.net) and examine "control.sch". D4, pulled down by an LED, is the "OI" signal. My solution to his exam question is this: - "Just connect /OE of both 28C16's to the inverted clocksignal, because than a valid value is ready to be read in". :: Ok, what did I win? ;)

I wonder “A+B” and “A PLUS B” is them same?

If all switches are on it tuk 1A only for the switches by 100 Ohm resisters...

Nice feature! This could be simplified by using 4 JK flip-flops and 4 momentary switches. Just use a push button bound to a bit position to toggle the single bit.

8:22 how this is used when A is allready in A thats silly function. is it atleast plus carry LOL and same on other mode output A so one is with carry and another no carry. silly desing have samethings other mode and function not same LOL thats why its 16 operation not 32. i not find a-b anywhere . i know its a+(bxor+1)

4:41 you left best thing explained. what happen A=1 B=1 is result 11111101. 1+1=2 and invert. wel logic havet to its sum inverted

Awesome bro

Brother we face some problem while performing A plush AB`(B bar)... Please help me.

I have build this computer during the time Ben did, but I used HC series chips instead of LS. HC differs from the LS series in the way that every input pin MUST have a pullup in order have a defined value every time. In fact, you should add pullups to the DIP witches as well. For the MAR and the RAM. The HC series 157's won't work without it. For the LS series, it is better to have them.

Hi What did you used to hook the 7 segment to program counter please ????

thank you sir! This also fixed my issue. I had this exact problem and I also would get the "RAM Overwrite" when I pressed the CLEAR button. Was driving me nuts! I added 1K pull up in same spot you did and also one on the programming leg. it fixed all my issues. Floating inputs are BAD!!!!!

active high and active low are different chip, what exactly this is because i connected not gate to output to get result in active high

Thanks for the information ☺️

if alu 1 A=b is high and alu 2 A=B is low then the total is A not = B, so joining both A=B's together will give a conflict between them

If the answer is 42, I really have to wonder if you're asking the right question.

Thanks for making this video. This fixed my problem too.

thank you, I am in the middle of a 20 hour print and I didn't check the status of the filament before starting and now it seems I might run out of it, so I was wandering if the filament sensor will work as expected.

Nice content & do more uploads pls👍

There is a INC A too

Very helpful, thank you!

Adding basically an RC filter on the CLOCK line the whole integrity of the signal is altered (in some designs you will find RC circuit to improve clock integrity but not the case here) From what I measured jitter is a big problem (and is amplified by the use of breadboards) when adding this "edge detector" and 161 from DS is quite sensitive to clock jitter. Best way is to use a digital edge detector. Ben may have avoided this because he uses rally high quality breadboards or he is just lucky to have marginal levels of clock jitter.

Have you tried building a version using veroboard ( en.wikipedia.org/wiki/Veroboard ) instead of breadboards?

Would you mind sharing the files for the 3D printed spool? Thanks.

I know this is an old video but adding the comment anyway In case anyone runs into this problem as well.. I had the double bounce on the clock cycle as well. I increased the capacitor size from 0.1 to 0.22 µF on port 6. That seemed to fix it. My guess was I was too slow to release the single step clock button.

Great videos. I’m building up the breadboard computer on pcb prototype soldering breadboards. Definitely more reliable than the non solderable breadboards.

I would say the resistor should be before the capacitor one end of the capacitor to ground and the junction of the 2 to the gate

Wow 🤩

Wow 😯

Wow, you did, going to well 👍

do you have a schematic for this online? It would be a great help

This is so great. Seven years ago when I was getting into orbital mechanics, I found David's great videos on the Orbiter simulation. Now I am getting into digital electronics, and who do I find again but the amazing David Courtney. Makes me wonder what's next!

If you put weird analog stuff into a digital circuit, you will get weird analog behaviour out of that circuit. Simple as that ...

Could you please let me know how the load is held in say floor no. 2? Wont the load free fall? What has to be done to hold the load in place preventing it against gravity? This is for a project for my son. Thanks

I had the same problems... put a Not Gate or two as a buffer, to isolate and drive the state change in other places. It seems the RC circuit makes other linked clocks iffy. Other things I've noticed is if you have any gates (AND, OR, NOT, XOR, etc ) need to pull any of those input either up or down depending on the logic family... TTL likes inputs to be pulled high using resistors. others (open drain?) like to have inputs or outputs pulled to ground with resistors. Maybe get the Datasheet for some of the chips in question and read through them again see what they recommend on each one. Another thing to note is there are strict requirements on power supply voltages for TTL logic, keeping the supply voltages in the range is important. =D

IT LOOKS TO ME LIKE YOR RAM INPUT IS FLOATING FOR A BRIEF MOMENT BETWEEN PROGRAMMING MODE AND RUN MODE...........LOOKS LIKE YOUR SWITCH NEEDS TO BE DEBOUNCED....OR YOUR RAM INPUT NEEDS TO BE SET WITH EITHER PULLUP OR PULL DOWN RESISTOR....IF YOU HAVE AN OSCILLOSCOPE...TRY TO SCOPE THE SWITCH TO DETERMINE IF SWITCH BOUNCE IS OCCURING.......OR SCOPE THE RAM INPUT PIN FROM THE SWITCH TO SEE IF SIGNAL BOUNCING IS OCCURRING WHEN SWITCHING MODES.........GOOD LUCK

Super 👍👍👍

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How to load a program into SAP 1 RAM like this LDA 9H ADD AH ADD BH SUB CH OUT HLT

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Great work, how about selling this PCB?

Sir how a program load to sap 1 RAM

This is microprogrmmed I don't know (I am unable to get practical example) how hardwired works I learnt in theory but practical example I am not aware, if you know kindly let me know

Thanks a lot , can you give me code and layout.

can u please tell me how does the elevator knows its postion

For me I had to put a 1k pull up to 5V on both the floating pin of the manual write push button, and the floating pin of the program/manual slide switch. Both of these floating pins connect to a 74ls157 and I guess it didn't like the floating haha. Thank you so much for the tips, it helped me solve my issue too! (Same issue as everyone else, where there was an accidental write when switching between modes)

Thanks for posting this! I decided to build this thing during the pandemic and I had the same exact issue, but the 1k pullup resistor on pin 14 of the 74LS157 stopped writing ghost values into RAM. So, thank you for posting the other video with the symptom as well as the detailed solution here. I suppose thanks are also in order for Steven and Paulo for inspiring the solution.

I had the same problem and I spent most of my day trying to solve it. Thanks a bunch everyone who contributed to the solution and of course to you David for making the videos!