Third and final attempt at the Altair project

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Postby vbriel » Apr Mon 13, 2009 6:45 am

Ok, just another note, I'm going to wirewrap up a board but I might not get to it until this weekend. I'm going to keep it simple, just the first 8 switches, all 16 address LED's and 8 data bus LED's. I'll add a run/stop switch and an examine switch so I will know if I can jump to memory.

I know that I can program the memory just by seperating the CPU from the RAM and having the uController assert the address and data. So, for this test I probably won't even hook up RAM. Once I get this to work, I will goto board and test.

Vince
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Postby vbriel » Apr Thu 23, 2009 11:00 pm

Well, still haven't had time to wrap up a board for tests but this weekend is looking very good to do some work. I'm almost caught up on orders and other personal stuff is done so it's time to work!

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Postby vbriel » Apr Wed 29, 2009 7:44 pm

Making my wirewrap board now. I have the power switch and input working, now I'm wiring pullup resistors to the CPU. Next I'll wireup the uController to the CPU. Tomorrow I'll wireup the LED's and see what we got.

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Postby AndyC » Apr Thu 30, 2009 6:29 pm

Any progress yet? I'd love to see some pictures.

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Postby vbriel » May Fri 01, 2009 2:47 pm

I just finished wiring up the "Basic" system. All it is, is the 8085, uController, 74LS373 latch for the data bus/address bus, an oscillator, and Bar LED display for the address bus. I just need to add a reset switch then I can write code to start trying to jump the address. I'll take a picture this weekend but it looks a lot like the Z80 wirewrap board I did except I don't have any databus leds yet and all address. It's easy to write data to RAM, so this test right now won't be doing that. Just JMP command. If I can do that, the system will be a go.

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Postby vbriel » May Sat 02, 2009 3:35 pm

Well, difficult but I have partial success. I am able to get the 8085 to jump to my address but not everytime. This means my timing is off a little. I'm only going at 8Mhz on my uController so I may add a crystal to go 16 and see if that helps.

This may be possible.

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Postby vbriel » May Sat 02, 2009 6:48 pm

Saturday update #2. Well, the little program I wrote puts the CPU at address $8833 most of the time. I'm trying to sort out why it doesn't work some times. But when it does, it is also stopping where I want at M1 instruction fetch cycle. This is perfect. I'm going to add a push button and see if I can add step now. After that, I'll look into adding some RAM and switches.

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Postby vbriel » May Sun 03, 2009 11:27 am

Z80 is not 100% compatible with the 8080, the 8085 is. Altair BASIC does not work on the Z80. The Z80 was easier to control and step but things are moving along. If I find time today, I'll hook up a button to work with singe-step. If I can single step and JMP at any point, I know this will work.

I'm still being a little cautious because the test program I wrote takes the CPU to address 8833 on power up and it works sometimes on power up, other times, I have to hit reset a few times. This could be because of the reset hold time, other issues such as wirewrap is not perfect. Still, a very low cost way to build a test board.

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Postby vbriel » May Fri 08, 2009 7:20 am

I keep getting close. The best I got was code that didn't work initially, but after I hit the stepped button once, it worked!?

I don't have a logic analyzer but I'm shopping for one now. I have to have one to do this. otherwise I'm stepping blind on this. I wouldn't be shopping for a logic analyzer if I didn't think this could be done.

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Postby vbriel » May Fri 08, 2009 5:00 pm

I bought an old HP logic analyzer on ebay and will have it next week to be able to continue this.

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Postby mfortuna » May Sat 09, 2009 8:31 am

Cool! 1650 model?
Mike

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Postby vbriel » May Sat 09, 2009 1:29 pm

Older. 1630G. I wanted the 1652 or better but had to settle for this one for now. My plan is to get a good USB one in the future. Right now, I need to get this timing down.

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Postby bugman » Jul Tue 14, 2009 3:06 pm

Just curious if you had an update on the progress. Its been awhile and I'm watching closely.

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Postby Aaron Teeling » Aug Fri 14, 2009 2:20 pm

Hey Vince,

Any more progress on the Altair?

Aaron
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Postby Des » Aug Mon 17, 2009 12:51 am

Hi

Yes I would also be interested to hear what is happening with the Altair kit project
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