Atari 800 Engineering Serial 26

[ClausB]

A look at the RAM cards showed 4K in slot 1 and 16K in each of 2 and 3. Both sizes used the same circuit board, dated 1978. They contained standard 4K or 16K DRAM chips and had jumpers to select the size. This was unlike the later 8K and 16K cards, which used different circuit boards and selected RAM in units of 8K.

Looking at the Atari 800 OS Manual and Listing, I noticed that the routine that figures out total RAM size does so by testing memory in 4K blocks. Shades of the prototype hardware?

The OS Listing shows evidence of the old prototype's memory map. There are these strange comments on page 78:

 

; "A" CART. ADDR'S ARE A000-BFFF (36K CONFIG. ONLY)
;
; "A" CART. ADDR'S ARE B000-BFFF (48K CONFIG. ONLY)
;

The first one gives the correct address range for the "A" (left) cart but refers to the old prototype 36K RAM size. The second one refers to the production 48K RAM size but give the wrong address range. In the 1st post, notice that the prototype left cart range was $B000-$CFFF. Maybe these comment lines were hastily edited when the memory map changed?

[Urchlay]

I just have to say it: I love this kind of digital archaeology. Keep it up!

[classics]

Very nice. If you did auction this off I imagine there would be some stiff competition for it.

 

Steve

[cephallus]

Thanks again for posting details/pics on this unit. Very interesting!

 

I agree with Steve; depending on timing (who's looking, etc etc), I could see someone paying some $$$ to own it. I'd personally love to see it end up somewhere that others could see it (museum display, or at least online museum display).

[ClausB]

I just have to say it: I love this kind of digital archaeology. Keep it up!

Yes, it is interesting, isn't it? Just wish I could find more early development documents and prototypes online. I've heard that someone in this forum has other prototypes, but when I asked for photos I got nothing.

 

I'd personally love to see it end up somewhere that others could see it (museum display, or at least online museum display).

What could be done with the photos and info posted above to make them more presentable or accessible?

[+kheller2]

Those ceramic early production chips are surely sexy!

 

The ceramic RAM chips are sexy. Those must have be very expensive back then.

[cephallus]

I'd personally love to see it end up somewhere that others could see it (museum display, or at least online museum display).

What could be done with the photos and info posted above to make them more presentable or accessible?

 

The pics/descriptions that you posted here are already fantastic! It's just that this is a forum...perhaps one of the "museum display" format sites (e.g. Curt's AHS site, etc) will pick them up and put them on display.

[cephallus]

Those ceramic early production chips are surely sexy!

 

The ceramic RAM chips are sexy. Those must have be very expensive back then.

 

I was kind-of surprised to find ceramic RAMs and CPU in an early (1982) c64 I opened today.

[fibrewire]

Necrobump - Nice machine!

 

Pics of "engineering serial 26" are earlier in this thread

[ClausB]

Here are full-res photos of old number 26's motherboard.

[ClausB]

Here are full-res photos of old number 26's motherboard.

 

Strange. This site let me upload the full 3Kx2K JPGs but when I download them, they are only 1200x900. So here are ZIPs of the JPGs:

26mc.jpg.zip26ms.jpg.zip

[ClausB]

 

Notice that the original cart connector had only 24 pins and the cart held 2 4K ROMs. That's 12 address lines, 8 data, 2 power, and 2 chip selects. No R/W line nor I/O select, so it was for ROM only, no RAM nor I/O, just like the 2600. Glad they fixed that!

[Rybags]

Is it downward compatible - noting that the extra signals are all at the edges of the final design ?

 

Although even if it was, the narrower edge means it mightn't align well to the cart port.

[ClausB]

No, it uses 4K select lines where the production cart slots have 8K selects. It could only address 8K of ROM at most.

[fibrewire]

Hey, collectors, is old #26 worth anything?

Looking at the label with the yellow to brown "800" and the outline "Atari" lettering makes it stand out as a collector's piece. Also the fact that the positioning holes in the top lid, and the fact that it doesn't look quite right make it very cool. Opening it up is where the gold is - I'd pay at least $1000 for it

[ClausB]

I've started to document the prototype 800 circuit exhibited in old #26, as it was before the modifications that made it compatible with production 800s. Attached is the partial schematic of the 1978 motherboard, based on Jerzy's drawing. It's not finished - some of the pin numbers are wrong - but the circuit is correct per my notes.

 

Notice the difference in RAM address decoding for 4K and 16K boards. Also notice the 4K ROM selects and the chip selects for POKEY and PIA. (See the memory map in the first post.)

 

 

For an unresampled GIF, unzip this:

800#26.GIF.zip

Edited July 12, 2012 by ClausB

[ClausB]

Some corrections and updates:

 

The LS138 decoder selects are corrected.

 

POKEY and PIA are selected by A10 (not A11 as shown previously) and by PCS from the OS board (which is /A11 NOR /SD). So A10 low selects POKEY (pages $D8-DB) and A10 high selects PIA (pages $DC-DF).

 

Pin numbers are corrected for all slots (except where left blank). Rybags' observation above was astute - the data and address pins are in the same order as on production carts.

 

800#26.GIF 2.zip

[ClausB]

Now the OS board with 4 2716 2KB EPROMs and the original I/O address decoding:

 

 

PCS has been renamed to PPSEL (POKEY / PIA select) and CTIA to ACSEL (ANTIC / CTIA select).

[ClausB]

Here's the 4K/16K RAM board. Notice the A/B jumpers so that one PCB could do both RAM sizes, as opposed to the production 8K and 16K boards which differed.

4K16K.GIF.zip

[Chris Strong]

This is exactly the sort of thing that I am most interested in with my collection (early 400/800 development, production testing, and field service gear).

 

This is the neatest 800 I've ever seen. I have several of the early (1979) release models, the ones with the tin card edge connectors and the female keyboard socket on the motherboard, but none like this. I have one from Atari HCD engineering that was probably like this when it was made, (there is no silver date code molded into the case as it is not a production model, but most of the components are very old) but its motherboard had been replaced with one from 1981.

 

I don't see the power board anywhere. Does it have the white SIO port?

Edited September 28, 2012 by Chris Strong

[ClausB]

I have not compared old #26's power board with production ones. I does have a black SIO connector, though.

[ClausB]

The PS board has no solder mask and was hand-soldered. The SIO connector is black.

 

Edited September 29, 2012 by ClausB

[ClausB]

Updated schematic:

 

[ClausB]

BASIC EPROM dumps:

BASIC.A000.4-18.txt

BASIC.B000.4-18.txt

[ClausB]

OS EPROM dumps:

OS3.6-15-79.D800.txt

OS3.6-15-79.E000.txt

OS3.6-15-79.F000.txt

d800.bin

E000.BIN

F000.BIN