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  #1  
Old 06-21-2007, 04:58 PM
Geoff Harrison Geoff Harrison is offline
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Default 88-4mcs

I just finished building Grant's 88-4MCS 4k memory board replica. I'm not sure if he's ready to release them yet, he didn't have the documentation ready but I talked him into letting me have one early.




As you'd expect, it's a beautifully implemented copy of the MITS board, well worth adding to the Altairkit 8800.
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  #2  
Old 06-24-2007, 12:11 PM
sje sje is offline
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Very nice.

How does the 88-4MCS 4 KB RAM board compare with the IMSAI 4 KB board? I assembled one of the latter and I recall that it had a cycle time of less than 450 ns (hence no wait states needed for a 2 MHz clock) along with a static (non dynamic) implementation. Oh, and the IMSAI card had those nifty red and green LEDs for the 1 KB protect feature.

Perhaps the 4 KB RAM card should be the default for the kit instead of the 1 KB card.

--------

Yes, I'm still considering ordering the 8800 kit. If it were the 8800b (with front panel) version, then there would be little hesitation.

How are the other cards (PROM and serial) coming along? I'd rather not have to scrounge around ebay to find these.
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  #3  
Old 06-24-2007, 11:06 PM
Geoff Harrison Geoff Harrison is offline
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Quote:
Originally Posted by sje View Post
Very nice.

How does the 88-4MCS 4 KB RAM board compare with the IMSAI 4 KB board? I assembled one of the latter and I recall that it had a cycle time of less than 450 ns (hence no wait states needed for a 2 MHz clock) along with a static (non dynamic) implementation. Oh, and the IMSAI card had those nifty red and green LEDs for the 1 KB protect feature.
Both boards use the same 2102 static RAM chips. Protection on the MITS board is at the board level instead of at the 1k bank level. And, you're right, those indicator LEDs on the IMSAI board are nice; there are no LEDs on the MITS board.

I populated the board with my own 2102s of unknown heritage and had a couple of memory errors when the board was up on an extender card. When it's plugged directly into the backplane, though, it's 100% reliable. I ran a memory test all day yesterday with no failures. One day when I have nothing better to do, I'll track down what's going on with the extender card, but I'm in no hurry.

Geoff.
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  #4  
Old 06-25-2007, 02:47 AM
Grant Stockly Grant Stockly is offline
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Quote:
Originally Posted by sje View Post
Yes, I'm still considering ordering the 8800 kit. If it were the 8800b (with front panel) version, then there would be little hesitation.

How are the other cards (PROM and serial) coming along? I'd rather not have to scrounge around ebay to find these.
I would like to find a blank 8800B display/control board. I have the interface board in blank form.

The other cards are beautiful. I have tested the 2SIO and PMC boards. I've used the 2SIO board as a CP/M terminal and have transfered disks with it. I've used the PMC along with an EPROM programmer to make 1701s.

The only one I am waiting on is the 88-ACR cassette interface board. The SIOB is fine, but the MODEM board that goes with it uses some hard to find pots. Any pot would work, but wouldn't fit right.

I'm in Alabama right now but will be home on Tuesday. Remind me then to take some pictures of the pot. If you can find one that fits I might have to give you a discount!

I only have a few pictures of the new cards. They have not been resized and I did not take them for "quality". They are just pictures that I happened to take before I left.

Here are some teaser pictures:
Shot of 4MCS with only 1k of ram
http://www.stockly.com/images3/070503-4MCS_2313.jpg

Various new cards (I only sell MIL sockets with the kits, I'm using cheap sockets on the prototypes)
http://www.stockly.com/images3/07050...oards_2314.jpg

PMC testing, comparison of vintage PMCv1 to replica of a PMCv0
http://www.stockly.com/images3/07051...roPMC_2336.jpg

Vintage and replica 4MCS
http://www.stockly.com/images3/07051...mpare_2345.jpg

PMC with wire wrap ZIF sockets installed
http://www.stockly.com/images3/07060...8-PMC_2387.jpg
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  #5  
Old 06-25-2007, 07:46 AM
sje sje is offline
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Concerning the extender card: I'd guess either mechanical wobble (especially without card guides) or finger connector tarnish. The latter was a recurring problem with the IMSAI cards. An occasional treatment of the contacts with a pencil eraser did the trick.

I am very encouraged that other boards are showing good progress. I don't mind keying in a small bootstrap, but toggling a 16 KB chess program is out of the question. So an SIO board is a minimum requirement (after memory). Alas, none of my recent machines has a serial port, but I've got a USB/serial converter from Keyspan that should work.

About the pots: if neither Digikey nor Mouser carry these, then I wouldn't know where to look. I recall that there were some smallish "dial a resistor" discrete pots that were available back then and might also be around today.

The 8800b full function front panel (not the turnkey version) is a big improvement over the original with better toggles, better graphics, a slow auto stepper, and an accumulator display. I do not recall if the updated front panel board is wire and signal compatible with all the original hardware.
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  #6  
Old 12-31-2008, 10:26 PM
Pops Racer Pops Racer is offline
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Location: Lakelands, NSW, Australia
Posts: 15
Default L1 and L3 ferrite beads on 4MCS

Hi all,

Just halfway through assembling my 88-4MCS. MITS instructions call for 2 ferrite beads. My kit came with 1 ferrite bead and that is correct as far as Grant's packing list. For now I will install the 1 bead on the +V rail (L1) and just a jumper on the GND line (L3). I assume these are for hash noise suppression and not super critical.

Cheers
Kelly
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