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The moment of truth came... without any smoke, but also without properly executing the program.
The oscar showed a nice steady heartbeat and timing signals on the bus, all at the right frequencies. the state codes showed that the processor was alternately fetching instructions and executing them, as it should. There was also activity on the data bus, as well as on the address bus. perfect, but why does the LED that is hooked up to the processor's single I/O line (very much like a microcontroller) not light up at all?
After some time of measuring and searching I thought that I found it. The lower address lines were connected in reverse order. Easy to fix.
So I switch on the power, the power LED lights up, and the second one stays dark. I was already reaching for the power switch when it starts to blink merrily. Exactly what the program in the EEPROM should do. I guess, I should look for a smaller capacitor for that power-on reset.
Here it is with both LEDs on at the moment the picture was taken.[^] It's a little hard to see on the picture because of the bright lamp.
Now come a few modifications before I can safely have a board made:
- Replace red LEDs (and all future displays) with blue ones. It's a High Elf, not a Dark Elf.
- Add a MAX232 level shifter and we have it talking to a PC in no time over the serial port and terminal emulation. Without a UART! The same signal that now blinks the LED can be used to emulate a serial port. Of course I will need a slightly different program in the EEPROM, but I already have that ready.
- Add another 8 bit register, this time set up as an output port. Then I have 24 address lines and can expand the (banked) memory up to 16 megabytes. More than enough for a little 8 bit processor.
- Throw out the EEPROM and replace it with a pin compatible RAM. Now the Zwölf would not have anything to execute at startup. But that already worked on the old Elf. The processor has a 'load' mode, that can be entered after a reset and allows to load bytes into memory via DMA. The old Elf simply used it's hex keyboard and 7 segment displays as DMA devices in load mode. Today I would simply let a PIC microcontroller control the processor's mode and copy the BIOS or whatever I want it to boot from a tiny serial EPROM into memory via DMA, reset again and then switch the processor into run mode. Maybe I should still keep the door open for traditional hex keyboards and seven segment displays. Blue displays, of course.
And then I can make the (first) board to get everything off the breadboard. And make room for all the fun stuff that will go to the second board.
One last thing: I found an easy way to get up to 8 processors on that bus without stepping on each other's toes. Zwölf II might actually be a multiprocessor system.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Cool beans, looks like you got Zwölf running like a singer sewing machine!
Monday starts Diarrhea awareness week, runs until Friday!
JaxCoder.com
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Except for the slightly bigger and faster memories it's actually very close to the original Elf from 1976. Six of those little processors brought the Galileo probe to jupiter, survived in its radiation belt for years and finally crashed the probe into Jupiter, so that it does not contaminate one of the moons. Especially not the moon Europa. They did not want a dead probe with 15 kg Plutonium in its nuclear batteries to crash there.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Yeah I read about that, pretty freaking amazing!
Good luck getting a board made. Do you plan on having any extras made?
Monday starts Diarrhea awareness week, runs until Friday!
JaxCoder.com
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Why not? But the second board is going to get more interesting. How about PS/2 ports for a mouse and a keyboard? Or an IDE port with two Compact Flash memory cards as SSDs? A MC6847 as graphics chip? A YAMAHA sound chip?
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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What I meant was like this[^] guy did with the Z80.
Monday starts Diarrhea awareness week, runs until Friday!
JaxCoder.com
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Great!
You should create kits for sale...
"The only place where Success comes before Work is in the dictionary." Vidal Sassoon, 1928 - 2012
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Like this one here - The Lounge
Realized there was an interesting note about VS 2020 way back then in this forum message, but it won't open now. 
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Try putting this in the Sugs & Bugs forum.
- I would love to change the world, but they won’t give me the source code.
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Try this link:
The Lounge[^]
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Jwalant Natvarlal Soneji wrote: - The Lounge
Your link works for me. 
Social Media - A platform that makes it easier for the crazies to find each other.
Everyone is born right handed. Only the strongest overcome it.
Fight for left-handed rights and hand equality.
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When it was first introduced, the web had been described as a "living document". Translation: It keeps changing. So...links stop working. If there's anything I've learned, it's to save (locally) anything I want to hang on to. Then nobody can take it away from me.
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dandy72 wrote: Then nobody can take it away from me.
Except for Murphy. And Chuck Norris.
"Five fruits and vegetables a day? What a joke!
Personally, after the third watermelon, I'm full."
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Murphy would have to get to my backups as well.
As for Chuck Norris, well...I guess I'll hand him my backups.
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This pops up sometimes. The official reason is that the database load is too high. Trying again later usually works.
What do you get when you cross a joke with a rhetorical question?
The metaphorical solid rear-end expulsions have impacted the metaphorical motorized bladed rotating air movement mechanism.
Do questions with multiple question marks annoy you???
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Brisingr Aerowing wrote: The official reason is that the database load is too high
Yes, we've all learned this month that getting a server and db to handle as many as 1600 requests, spread over a couple of hours, is hard!
You're right. The OP's link didn't work for me a while ago, but it does now. Looks like an error page is needed, telling people to try again.
I wanna be a eunuchs developer! Pass me a bread knife!
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While reading in the lounge I got the following ad at the top of CP:
It's the greatest ever! So relevant. I was dreaming about a nice bucket of fried chicken and this totally relevant ad popped up. 
https://i.stack.imgur.com/8OpMz.png[^]
How do those CP techs do this? Amazing technology that is surely infused with AI. 
I am definitely going to start a Fried Chicken Franchise (that isn't a franchise)! I know this is a sign. 
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The ads are targeted at your browsing history.
Be glad it picked your "bucket list" this time - one different letter and the ads would be ... um ... 
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
AntiTwitter: @DalekDave is now a follower!
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OriginalGriff wrote: The ads are targeted at your browsing history.
That makes sense.
I've been searching "kripsy chicken" and "krunchy fried" all day. well, not just all day, all week.
EDIT
DAng! forgot this Computer-related joke:
Also, I've recently written an algorithm that does a "shortest distance to fried chicken". It's an app so you can just get in your car and it tells you where to go.
Actually, that app would probably make Billions!! Maybe even hundreds of thousands.
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raddevus wrote: Also, I've recently written an algorithm that does a "shortest distance to fried chicken".
What a coincidence! Last week I taught my CS class the Travelling Chicken and Chicken's Tour algorithms.
/ravi
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Ravi Bhavnani wrote: Last week I taught my CS class the Travelling Chicken and Chicken's Tour algorithms.
I wish I could've been in that class! I was busy building a web site for this guy: Super Chicken - Wikipedia[^]
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OriginalGriff wrote: The ads are targeted at your browsing history.
True.
Had you been searching for fish & chips shops, you would have been redirected to codproject.com.
I wanna be a eunuchs developer! Pass me a bread knife!
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Indeed: I was searching for young ladies in education, and got directed to CoedProject.com
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
AntiTwitter: @DalekDave is now a follower!
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I was searching expert ways to change my gender and found myself being directed to ExpertsExchange.com. Weird... what does programming have to do with gender reassignment!? 
/ravi
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