Museum restoration of 8800

[philrrtx]

Originally Posted by marty

Hi PHIL:
Could you please post the programs you are using here for the rest of us ????
Also, I have not had any problems with any of my 4k memory cards...
have you tried each card at all the addresses that you intend to use,,, maybe one or more is mapping to more than one address... THANK YOU Marty

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 negated, so it should be putting data on the bus, yet it looks like the bus is floating. We have decided not to worry about fixing it at this point. The 12K we have working is sufficient for our purposes.

The test programs for the 3P+S I/O board I have been using are in the documentation I found for it on Dave Dunfield's site. See http://www.classiccmp.org/dunfield/s100c/ptco/3pps.pdf

Here's the memory test program I wrote:

                     INSTRUCTION
LABEL	ADR	OCTAL		MNEMONIC	DESCRIPTION
	000	052 051 000	LHLD COUNT	Get number of locations to write
	003	353		XCHG		Move to DE registers
	004	052 053 000	LHLD START	Get starting address
LOOP	007	072 047 000	LDA BYTE1	Get first byte to write
	012	167		MOV M, A	Write in memory address
	013	226		SUB M		Read memory and subtract
	014	312 022 000	JZ CONT1	OK if zero
ERR1	017	303 017 000	JMP ERR1	Error if loops here
CONT1	022	072 050 000	LDA BYTE2	Get second byte to write
	025	167		MOV M, A	Write in memory address
	026	226		SUB M		Read memory and subtract
	027	312 035 000	JZ CONT2	OK if zero
ERR2	032	303 032 000	JMP ERR2	Error if loops here
CONT2	035	043		INX  H		Increment write address
	036	033		DCX D		Decrement count
	037	172		MOV A, D	Check if DE=0
	040	263		ORA E		       by ORing D with E
	041	302 007 000	JNZ LOOP	Go around again
GOOD	044	303 044 000	JMP GOOD	Good if loops here
BYTE1	047	252				First byte to write = 10 101 010
BYTE2	050	125				Second byte to write = 01 010 101
COUNT	051	323 037				Count = 16339
START	053	055 000				Start address

START must contain the first location past the program. COUNT must contain the total memory you have available minus the length of the program (remember, least significant byte first). The test is good if it loops at GOOD. An error has been detected if it loops at either ERR1 or ERR2.

[Forbin376]

Hi Phil,
“I was there when…” in high school we saw the ad for the MITS Altair 8800 in Popular Electronics and all wanted one. Well, I built mine in 1976 as a senior high school electronics project and it is still running today. I went on to sell them and have been (and still am) involved with computers.

The boards you have are the 88-S4K, or 4K Synchronous Dynamic RAM cards. These cards were created by MITS and actually sold for near cost (without the memory chips) to owners of the ill fated 88-MCD or Memory Card Dynamic RAM. These original cards were so badly designed that you could measure 200mv of noise from one side of the card’s “ground” plane to the other. MITS offered these later boards as an “apology” to all of us who had purchased the original cards. They (MITS) gave dynamic RAM quite a bad name and it was shunned in the later Altair/S-100 bus world. The newer 88-S4K cards are a much better design and were fairly temperature stable. However if you have the opportunity to replace them I would recommend it.

About the voltage regulator on the +8V – this was part of a power supply upgrade and is part of the difference between an “Altair 8800” and an “Altair 8800A” – nearly all of the “A”’s have this modification.

You may find this site of interest:
http://frankbarberis.tech.officelive.com/default.aspx

Frank

[philrrtx]

Originally Posted by Forbin376

Hi Phil,
“I was there when…”

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 more fully, so I've left it as is, mostly working.

As noted in an earlier post on this thread, we are missing the case and dress front panel for the one we have. I have not been able to get any response from Grant, via either direct e-mail or forum private message, about whether he would sell us those items so we can complete our restoration.

Instead, our exhibits expert has said she can duplicate the front panel for us, so we are waiting on that.

[TomL_12953]

Originally Posted by philrrtx

COUNT 051 323 037 Count = 16339

Maybe I'm not understanding something. 16339 should be 723 037 octal (reversed bytes)

So what's the 323 037?

Tom L

[marty]

Hi Tom;
The highest bit on an Altair or Imsai (64K memory) will only allow for a 3 in the left side of the octal number, such as 377.
THANK YOU Marty

[TomL_12953]

Originally Posted by marty

Hi Tom;
The highest bit on an Altair or Imsai (64K memory) will only allow for a 3 in the left side of the octal number, such as 377.
THANK YOU Marty

Ah! So with my 62K RAM, I'd have 62*1024 = 63488 - length of program (45 bytes) = 63443, convert to octal = 173723, reverse bytes = 723 173 mask off upper bit = 323 173

Is this right?

Thanks for your patience!

Tom L

[marty]

Hi Tom;
I am not good with Arithmetic and conversions, so I'll check it on my machine, and see if it flies, I have 64K on my machine...
THANKS Marty

[TomL_12953]

Originally Posted by marty

I have 64K on my machine...
THANKS Marty

You don't have any ROM at all? I have a 64K static RAM board but I also have I have the 88-PMC EPROM board that takes the top 2K of address space. I'd really miss it if I didn't have the Multi Boot Loader up there so I don't have to key in the bootstrap every time for paper and cassette tapes! I also have VTL-2 and the DBL (since I don't have a disk system, I won't be using that for a while) as well a monitor.

Tom L

[marty]

Hi Tom;
I tried it on my machine and it does the same thing as the origional program, it seems to work ok, it loops on the final loop indicating it ran ok... I want it to jump back to start, and it doesn't so I need to look into that..... but that will be later.....
THANKS Marty

[philrrtx]

Originally Posted by TomL_12953

Ah! So with my 62K RAM, I'd have 62*1024 = 63488 - length of program (45 bytes) = 63443, convert to octal = 173723, reverse bytes = 723 173 mask off upper bit = 323 173

Is this right?

Thanks for your patience!

Tom L

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, split it into two eight bit bytes, then translate each of those into octal (it's a heck of a lot easier to do in hex, but the spacing of the switches on the Altair makes that more difficult to enter—works nicely on the IMSAI if you have your switch paddles grouped in fours instead of threes).