Atari 815 for sale on eBay?

[ijor]

The links you provided to the source code and pictures tells you enough to back guess what most of the parts could be. They used a Motorola chip for serial communication and three PIAs. Two of the PIAs would probably be 6520s and the third a 6532; They may be Atari numbers but they would refer back to those chips. A 6532 may explain the 1/2 page of stack space. $FF RAM at page zero so that would probably be an another 24 pin DIP. In a cursory look at the info, I didn't see anything that couldn't be reproduced even if there was a custom part.

 

It is quite interesting. It is a pity that the schematics are not available, and that the original commented source provided by Curt is not complete.

 

From what I can tell, the 815 doesn't use a dedicated FDC chip, but it does use some hardware logic. The Motorola 6852 is a SYNCHRONOUS serial device. It is used for serially transmitting and receiving the drive data. When writing, the CPU transmits already MFM encoded data and clock. It takes two bytes to encode clock and data for each data byte. Probably there is no write precompensation.

 

But when receiving, there is external logic that provides PLL and data separation. The CPU reads data already decoded. Decoding by software probably would be too much for the CPU, and an external PLL to at least provide the serial clock is needed anyway. The 6852 SYNC char feature is used for detecting the byte boundaries.

 

This (sorta) explains why it is DD only, which means zero compatibility with 810 original disks. In first place the hardware must be changed to decode and implement data separation at FM (Single Density). It can't be done with just a ROM modification. But what probably is most important, is that the SYNCH mechanism can't be used reliably with standard FM marks that don't include the 0xA1 sync bytes as MFM does.

 

There is an additional interesting trick used. By convention, disk data is serialized MSB first. This is the so called IBM compatible format implemented by standard FDC chips. But the serial 6852 chip is LSB first. So according to the commented source, for compatibility, the data bus is wired in the reverse order to the 6852!

[Tempest]

I'm amazed they actually MADE a professional manual for it. Given they only did a pilot run I'd assume they just had a preliminary typed manual or something.

[+DrVenkman]

I'm amazed they actually MADE a professional manual for it. Given they only did a pilot run I'd assume they just had a preliminary typed manual or something.

 

Having creative work professional laid out and four-color printed took a LOT of lead-time back then; I suspect stuff like that got done early for most products, which explains the common practice of printed errata sheets included with many products of the day. So the stuff would've been sent to the printer well before the decision was made to cancel the product after just the pilot run.

[+MrFish]

BTW... that 815 manual is incomplete; either Curt missed scanning some pages or he just didn't have them to scan.

 

It looks like he just missed the back side of about six pages, because you've got 1, 3, 5, 7, etc.

[ricortes]

 

It is quite interesting. It is a pity that the schematics are not available, and that the original commented source provided by Curt is not complete.

 

From what I can tell, the 815 doesn't use a dedicated FDC chip, but it does use some hardware logic. The Motorola 6852 is a SYNCHRONOUS serial device. It is used for serially transmitting and receiving the drive data. When writing, the CPU transmits already MFM encoded data and clock. It takes two bytes to encode clock and data for each data byte. Probably there is no write precompensation.

 

But when receiving, there is external logic that provides PLL and data separation. The CPU reads data already decoded. Decoding by software probably would be too much for the CPU, and an external PLL to at least provide the serial clock is needed anyway. The 6852 SYNC char feature is used for detecting the byte boundaries.

 

This (sorta) explains why it is DD only, which means zero compatibility with 810 original disks. In first place the hardware must be changed to decode and implement data separation at FM (Single Density). It can't be done with just a ROM modification. But what probably is most important, is that the SYNCH mechanism can't be used reliably with standard FM marks that don't include the 0xA1 sync bytes as MFM does.

 

There is an additional interesting trick used. By convention, disk data is serialized MSB first. This is the so called IBM compatible format implemented by standard FDC chips. But the serial 6852 chip is LSB first. So according to the commented source, for compatibility, the data bus is wired in the reverse order to the 6852!

 

Could be based on the earlier EXORciser design.<???> http://www.exorciser.net/personal/exorciser/Exordisk_II.pdfThere are some obvious changes I think, like Atari using the 6520 vs the 6821 and I'm guessing a 6532 because they had a ton of them from the VCS. Ditto for 6507, although I didn't bother looking close enough to see if it was a 6507 or 6502, vs. 68xx! For everything else, I'd bet it was a close copy of the Motorola design.

 

Oddities abound and make me kind of giggle to myself. The 815 it allowed for 80 track drives which at first glance made me wonder what they were getting at. I mean the ST had those 360k SSDD 3.5" drives. Then I look at the EXORciser and see it could be configured for 8" drives<actually IIRC they were 77 tracks> and it almost makes sense. Looks like it is time for another candidate for a podcast!

[Mechanicjay]

I wrote an 815 off my bucket list years ago, because they're so rare.

I should stop complaining about the going rate for an ATR 8000!

[ijor]

 

Could be based on the earlier EXORciser design.<???> http://www.exorciser.net/personal/exorciser/Exordisk_II.pdfThere are some obvious changes I think, like Atari using the 6520 vs the 6821 and I'm guessing a 6532 because they had a ton of them from the VCS. Ditto for 6507, although I didn't bother looking close enough to see if it was a 6507 or 6502, vs. 68xx! For everything else, I'd bet it was a close copy of the Motorola design.

 

It seems at least, inspired in that Motorola design. Hard to say how close it is without the schematics. But note that the mentioned Motorola design is FM while the 815 is MFM. The bitrate is still the same in both, because it was common to use double bitrate with 8" disks. But the encoding is different.

 

[Ransom]

Shockingly, no one's bought the broken 815 for $2500 yet.

[Bryan]

 

It is quite interesting. It is a pity that the schematics are not available, and that the original commented source provided by Curt is not complete.

 

 

If anyone wants to loan me an 815, I'll make schematics and clone the PCB's for it.

[tep392]

It looks like someone bought the 815. Was it anybody here?

[Ransom]

That's strange. It doesn't come up in the Completed or Sold searches.

[tep392]

That's strange. It doesn't come up in the Completed or Sold searches.

That is strange. But it does show as sold in my watch list.

[Timothy Kline]

You can view the listing here.

 

--Tim

[Ransom]

Sure, you can view the completed item, but if you go to Advanced Search and choose "completed listings" and type 'Atari 815 Dual Disk Drive' into the search field, you get back a bunch of items, but not the 815. Same for sold items.

 

Someone who does a lot of selling may know what that means. Does that mean the seller ended the auction prematurely without selling it through eBay (a possible side deal)?

[Timothy Kline]

Sure, you can view the completed item, but if you go to Advanced Search and choose "completed listings" and type 'Atari 815 Dual Disk Drive' into the search field, you get back a bunch of items, but not the 815. Same for sold items.

 

Someone who does a lot of selling may know what that means. Does that mean the seller ended the auction prematurely without selling it through eBay (a possible side deal)?

 

Now you have me wondering, too.

 

--Tim