Atari IC Questions

[+Larry]

Looking at the IC's at Best Electronics I see

 

1) There is a separate part number for the 600XL OS. I thought there was one OS for all XL and XE (although different revisions nos.). Does anyone know the difference(s)?

 

2) I see only one GTIA -- used for both 400/800 and XL/XE?

 

3) CO61618 is the XE MMU. What is CO25953?

 

4) What function does Freddie perform?

 

-Larry

 

 

[Mathy]

Hello Larry

 

CO25953 is the gate array that switches over A14 and A15.

 

Freddy does what some small ICs did in the XL. Like create the CAS and RAS signal IIRC.

 

Sincerely

 

Mathy

[Kr0tki]

1) Each OS revision was a different mask ROM, so it had to have a different part number. "600XL OS" in this case refers to XL OS rev. 1.

 

Revision differences are documented to a degree in the source package posted somewhere in this thread.

 

2) Yep, the GTIA was the same in all Atari models. (Well, there actually were three different versions, for NTSC, PAL and SECAM.)

[+Larry]

Thanks, guys!

 

-Larry

[_The Doctor__]

It is kind of a shame that no one has thoroughly examined and tried all the possibilities of what freddie might do or be capable of.... quite a bit of real estate.....

[Bryan]

The problem is that Freddie is glue logic so it's pretty much invisible to the programmer.

[_The Doctor__]

Freddie must have had some things important enough to hide from us then, too bad we still don't know.

other than some simple logic we know it has a hand in address decoding and may help divide up the processor's address space into ram rom and the input output and may touch on helping interfacing external devices...

does it provide buffers to protect outputs from overload, or protect sensitive inputs from static damage.

is it robust enough to handle voltage level conversion when interfacing cmos to ttl?

It might also use less juice to get things done....

 

anyone good with acetone and nitric acid having decent camera equipment wanna strip a freddie down and compare it against what is known?

[Kyle22]

Freddie is just some TTL logic chips put together. It is not programmable. Here: http://www.atarimax.com/jindroush.atari.org/data/achips/freddiei.gif

is the internal schematic of Freddie.

[_The Doctor__]

Nice digging kyle! You come thru yet again.

 

Good info, now fried freddie xe's will be a cheaper and somewhat simple fix!

Edited September 2, 2015 by _The Doctor__

[Rybags]

Yep, nothing tricky there... and the MMU + EMMU I believe are nothing more than PLA types.

 

Compare the memory select, refresh, row/column logic with the XE vs what the 800 had, on the 800 it probably took up 5 times or more the space.

[ClausB]

Here's the Freddie datasheet. There's more there than Jerzy shows, like support for an alternate PORTB.

 

http://ftp.pigwa.net/stuff/collections/Atari%20documents/Custom%20Chips%20Datasheets%20and%20Databooks/Atari%208-bit%20computers/freddie-mcu.pdf

[576XE]

And how we can change dumb logic to be not so dumb?

 

Please look at these facts:

VBXE totally replaced video.

RAM 320XE totally replaced Extended RAM.

...

 

I think that it's Atari step forward!

Let's Go Ahead!

[_The Doctor__]

Here's the Freddie datasheet. There's more there than Jerzy shows, like support for an alternate PORTB.

 

http://ftp.pigwa.net/stuff/collections/Atari%20documents/Custom%20Chips%20Datasheets%20and%20Databooks/Atari%208-bit%20computers/freddie-mcu.pdf

so more work IS needed. I wonder what else will be found?

someone here just might enjoy stripping a chip after all..... chip torturer!

Edited September 3, 2015 by _The Doctor__

[Kyle22]

The PORTB stuff is on pins 6 and 7. Latch Enable and Output Enable are not connected to anything on any schematic I have ever seen.