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

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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.

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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..

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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

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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

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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 :-)

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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

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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

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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...???

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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

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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

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John, Great trouble shooting! You really spotted the problem there when the 74LS10 input was lifting the logic. You have nothing to apologize for, it was not a well thought out design. It should never

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Yeah... I'm a bit of an amateur when it comes to electronics, so when it comes to faults I can just about figure out the logic of things. Nice going on finding a fix for the errors in my ways. Will ha

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Tor-Eirik - thanks for sharing your design! I had a lot of fun and learnt a lot by building it!

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Tor-Eirik Lunde wrote: No worries, mate. Hobbies are all about fun and new experiences. We learn more from our mistakes than from our successes. :-) On the 74LS10: One way to avoid fix it is to use a

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I am thinking R3 at 47K is too high of a value for an 74LS10, cmos would be fine. Try dropping the value a bunch (maybe 3.3K) or swap the 74LS10 to something like a 74HCT10. The 74LS10 circuit is show

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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

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John, Nothing for you to apologize for, looking at the published BOM for the RC1802, it called for LS chips so perhaps this is a design flaw and we should be using HC instead. If we use LS chips, shou

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It doesn’t use TILs, it uses a common cathode 7-segment LED display.

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MC14495 latch and hex to seven segment decoder

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