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Search: Posts Made By: philrrtx
Forum: Altair 8800 08-07-2009, 10:29 PM
Replies: 29
Views: 103,868
Posted By philrrtx
Looks like my 323 was correct, but the second...

Looks like my 323 was correct, but the second byte should have been 077 instead of 037.

In Tom's case, I get 323 367. You can't mask off the bit; you have to write octal 173723 out in binary,...
Forum: Altair 8800 08-07-2009, 09:05 PM
Replies: 29
Views: 103,868
Posted By philrrtx
It's a typo; that's what it is. You are correct....

It's a typo; that's what it is. You are correct. It should be 723 037.

Phil
Forum: Altair 8800 08-06-2009, 09:30 PM
Replies: 29
Views: 103,868
Posted By philrrtx
Three of our four S4K memory cards are working...

Three of our four S4K memory cards are working OK. Originally all four of them were, but one stopped putting data on the bus for some reason. I was unable to find a schematic for it to troubleshoot...
Forum: Altair 8800 03-30-2009, 03:40 AM
Replies: 29
Views: 103,868
Posted By philrrtx
Programs and things

The failing card is correctly detecting its starting address, which can be viewed with a scope at the test point just left of the address switches. I also can see the bus driver disable signal being...
Forum: Altair 8800 03-24-2009, 03:50 AM
Replies: 29
Views: 103,868
Posted By philrrtx
Unhappy One step forward, two steps back

I finally got the sense switch read problem sorted out. It turned out to be the 74L30 chip that detected all ONEs on A15-A8 (the I/O device address). I didn't have a 74L30 ready at hand, so...
Forum: Altair 8800 03-09-2009, 09:12 PM
Replies: 29
Views: 103,868
Posted By philrrtx
Smile Thar be I/O

After a few bumps and stops, I have the Processor Technology 3P+S I/O card working via an RS232 interface with an LSI ADM-3A CRT (a nice terminal contemporary to the Altair). Whoever had this card...
Forum: Altair 8800 02-28-2009, 02:45 AM
Replies: 29
Views: 103,868
Posted By philrrtx
Thumbs up Instruction set annoyances

I reached the point where I wanted to run a memory test program and discovered two very annoying deficiencies (IMHO) with the 8080 instruction set.

The first annoyance is that the DCX (double...
Forum: Altair 8800 02-21-2009, 08:02 PM
Replies: 29
Views: 103,868
Posted By philrrtx
Progress report

Actually, I misspoke when I said they were the 4K dynamic boards. They are actually 4K synchronous boards, which I believe use static RAM chips. In any event, I finally figured out how the address...
Forum: Altair 8800 02-10-2009, 04:01 AM
Replies: 29
Views: 103,868
Posted By philrrtx
A little progress

Got my replacement ST1-1 switches in and replaced the three broken ones in the upper row. I still haven't found anyone with the ST1-3s in stock, and APEM, the current manufacturer, was less than...
Forum: Altair 8800 01-31-2009, 03:07 AM
Replies: 29
Views: 103,868
Posted By philrrtx
Exclamation Schematics and switches

Thanks Tom. I found the schematic for the 4K dynamic memory board there. The 3P+S I/O board turns out to have been made by Processor Technology. So far I haven't found a schematic for it on line. ...
Forum: Altair 8800 01-28-2009, 07:32 PM
Replies: 29
Views: 103,868
Posted By philrrtx
Museum restoration of 8800

I am starting the restoration of an Altair 8800 for the Goodwill Computer Museum in Austin. It was discovered about half-way through the Goodwill computer recycling process, and despite our best...
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