The 47K resistor in the wired-OR is great for CMOS logic but TTL, even LS TTL, draws more current. A quick check of a data sheet shows input current when Vin=0.4V of -0.4mA. Which will create quite th

#memory #ELF

Yes, swapped in a new chip. Voltage is 4.85v.

#memory #ELF

John — With both the74LS10 chip out and with it in, check the voltage across GND (pin 7) and Vcc (pin 14) just to make sure you’ve got good power to the chip. And, I think you’re also saying in your f

#memory #ELF

I unsoldered and replaced D6, D7 and the 74LS10. Interestingly the LOW signal at pin 10 of the 74LS10 is exactly as expected. However, when the chip is inserted, the logic probe won’t give a high or l

#memory #ELF

When you're NOT in load mode, the LOAD_N2 line should be low (until an OUT instruction pulses N2). The strobe to the LED shouldn't be happening all the time. Check that diode OR gate...???

#memory #ELF

Display: I may be looking at something different: https://github.com/tebl/RC1802-Cosmac-ELF/raw/master/RC1802%20UI/export/RC1802%20UI.pdf The data latch for the displays is driven by signal _STROBE_ w

#memory #ELF

Current theory (may be nonsense ;-) - Display issues Problem: I can’t display specific values on the LED displays using the 1802 out command, as expected. * The original design the RC1802 used TIL311

#memory #ELF

John, you might just want to try comparing that circuit with the original ELF circuit and see if anything is missing/wrong.

#memory #ELF

Oh, not getting this working is like an itch in my brain, and its making me careless. There is a pull up, and as far as I can tell the flip-flop reset is working fine. I did find one other clue though

#memory #ELF

Hi John, Is the designer of that ELF available? Is there any ECO or Error fixes listed? I wish I had time to build the same project, but I've got too many projects piled on my bench and more on the sh

#memory #ELF

I wish I had another kit to check the CPU signals :-) I might have to get the Membership Card after all! At the moment I’m suspicious that when I set up the system to load a byte into memory and press

#memory #ELF

As I feared - I don’t see that. Just 88, so the my guess is that display is being “updated” every cycle. Time to look at the cct diagram a little more :-)

#memory #ELF

Hi John, The neat thing about 1802 OUT instruction is that it increments the X Register. So, if you make the X register the same as the PC register, not only will it point to the next byte (since the

#memory #ELF

Could someone tell me what the simplest program to a display a value on the 2 hex displays would be? My experiments are not working, which makes me thing I do have another hardware issue on my hands..

#memory #ELF

joshbensadon wrote: Ain't that the truth! I think we all suffer from it. We stare at what's in front of us, and assume that's the whole picture. But fail to look to the sides or consider the alternati

#memory #ELF

Greg, Everything is hard before it's easy. This is the exact problem I seem to have at work... it takes me 4 hours to write up something that is read in 4 minutes and the boss thinks I'm slacking off.

#memory #ELF

What amazes me is, when I finally figure out what a problem was, it seems so obvious that I don't understand why I didn't figure it out a lot sooner. This seems to have been a pattern for me for decad

#memory #ELF

That's the spirit! I do very much the same when trouble shooting.... turn stones, poke it with a stick, etc. Besides, it's a great programming exercise.

#memory #ELF

Yes, the CPU is running says the logic analyzer, and signals seem present. A friend is also building the exact same kit, so when that is complete and we can rule out more of my construction errors. In

#memory #ELF

John, Check the RX pin at the 1802, does it get a pulse? What character are you sending for Autobaud? This might matter? Read the monitor documentation. I know capital 'U' is one of my favorites becau

#memory #ELF