Final assembly...

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Re: Final assembly...

Postby BillO » February 20th, 2021, 1:01 pm

I had a go at this this morning.

I reduced R42 from 4K7 to 3K9 and reduced the effective resistance driving the clock phases from 235 ohms to 167 ohms. Here is the result.

td1 55 ns
td2 120 ns
td3 135 ns
tr 13 ns
tf 7ns

Pulse widths in picture below.

Behavior is the same though. if the 2SIOJP is the last card on the MB, it receives spurious characters. If it's between 2 cards it's fine.

2-ph-clk-new.jpg
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Re: Final assembly...

Postby AltairClone » February 20th, 2021, 4:18 pm

I assume you’re still using AMON on the 2SIOJP? If so, then if the “Status Disable” switch is on, turn it off. Then make sure your system RAM stops before the start of your AMON PROM (typically F800). Let me know if that stops the problem.

Mike
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Re: Final assembly...

Postby BillO » February 21st, 2021, 10:05 am

Still using AMON on the 2SIOJP.

The SD switch is in the closed position (0). If I open it, the monitor won't boot at all.

My 2SIOJP came with the 4K EPROM so I have RAM set to end at EF00. I set that with the ROM switches on FDC+ board set to EF00 with the ROM disabled and the RAM enabled and set to start at 0000.

I was playing around with some to the DIP settings and now things seems to be working better. Here is how I have the 2SIOJP set (using O for open and C for closed)
Code: Select all
      8 7 6 5 4 3 2 1
SW2   O O C C C O C C

SW3   O C C O O O O O
Maybe there was a dirty dip switch causing me some trouble.

And the FDC+ set like this (using D for towards bottom of board and U for towards top of board):
Code: Select all
      8 7 6 5 4 3 2 1
RAM   D D D D D D D D

ROM   D U U U D D D D


I'd like to try booting CP/M from the serial server. Any suggestions on how I should set things?
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Re: Final assembly...

Postby AltairClone » February 21st, 2021, 10:43 am

Your switch settings look reasonable on both boards. How were they set before when you were having problems?
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Re: Final assembly...

Postby BillO » February 21st, 2021, 11:30 am

Pretty much the same way as far as I can recall. I just tried some random settings to see how the behavior changed then went back to these settings then things just got more stable. The only place the 2SIOJP does still give me problems is if is in slot 9. Perhaps a bad solder joint on that slot.

So, I disabled the ROM on the 2SIOJP, enabled the ROM on the FDC+ and set it to F800.

From their I was able to invoke the FDC+ monitor and ALTMON. I started the serial drive server with the CP/M22b image then did a hard reset on the 8800c. Then I set the address to FF00, examine and run. However all I got on the console was an endless series of capital "C". I used the FDC+ monitor to set the serial disk baud rate to 230K and tried again. Same thing.

Am I missing a step?

EDIT:
Okay, stupid me - I had put the FDC+ into slot 9. I don't know what I was thinking. Put it into slot 7 and everything is now working just dandy.

*** I'm running CP/M on a 8800 remake!***

Cool.
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Re: Final assembly...

Postby AltairClone » February 21st, 2021, 11:37 am

I assume you’ve set the drive type switches on the FDC+ to 7 and cycled power?

By the way, with the configuration as it is right now, out the 2SIOJP in slot 9 and see if the problem crops up.

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Re: Final assembly...

Postby BillO » February 21st, 2021, 11:48 am

Drive type is set to 7. I did that as soon as I got the board as I have no 5.25" or 8" drives at all.

Okay, I tried the 2SIOJP in slot 9 and I don't seem to have an issue with running CP/M at all, but with the FDC+ in slot 9, it's a no go. I just get all those "C"s.

There must be something wonky with slot 9. The only way I can run everything properly is to not use it.
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Re: Final assembly...

Postby BillO » February 21st, 2021, 12:10 pm

With the 2SIOJP in slot 9 I can run ALTMON and CP/M but not AMON.
With the FDC+ in slot 9 I can run ALTMON or AMON but I can't run CPM.
If I avaoid slot 9 I can run everything.

Here it is on my project filled bench. That unit to it's right is a 6502 machine called the OSI model 600.

Excuse the messy power entry. I am awaiting the arrival of a panel mount fuse holder to tidy that up. As it's configured it consumes about 190mA @ 120V or about 23W. Quite a bit less than the original I suspect.

IMGP9824s.jpg
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Re: Final assembly...

Postby AltairClone » February 21st, 2021, 3:58 pm

Sounds like good progress!

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Re: Final assembly...

Postby BillO » February 21st, 2021, 5:52 pm

And in no small part thanks to you Mike on several levels.

Thanks for your patience.

Thanks for your help.

And, thanks to you and the other enthusiasts that made this possible.

Great community!
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