Questions about the Atari 1450XLD from a fan who dreamt of having one

[ldelsarte]

I am very intrigued by the 1450XLD, its self-test and boot options. It is a fantastic piece and yet (almost) totally inaccessible to a collector. For me, the faster built-in floppy drive is the real game-changer.

But I wonder how it is supposed to be used. Let me explain.

 

When you want to boot with an (external) floppy drive, in theory, you should:
1. Remove any floppy disk currently in the drive
2. Turn on the floppy drive
3. After a short initialization, insert the diskette and close the latch
4. Turn on the computer (with or without the BASIC cartridge or the "Option" key)
If you want to boot without a floppy disk drive, just don't turn it on. Turn on the computer (with or without the BASIC cartridge or the "Option" key)

 

I may have seen incorrectly, but I have the impression that there is only one power switch on the 1450XLD. So, you turn on the computer and its built-in floppy drive at the same time. This is why the OS is modified to not display "BOOT ERROR" right away and wait for a floppy disk to be inserted.
The "Introduction to DOS 3" manual seems to indicate that you only have to close the latch to start the boot process. But I seem to remember screenshots that show a message prompting the user to press "RETURN" to start the boot. Which of these is true?

 

I also wonder: can you boot without the floppy drive, by disabling it? What happens if you press "RETURN" or close the flap without a floppy? "BOOT ERROR" or something else?
By the way, does the floppy drive stay on all the time?

 

Similarly, if I imagine the case where an external floppy drive is set to D1: and plugged into a 1450XLD. At boot time, the OS will first look for D1: on the parallel bus before looking on the SIO bus, right?

 

A recent video of a 1400XL allows you to hear the Votrax during the self-test launch and to see this re-worked version with a blue background in some tests.

 

 

My point: Is there somewhere a video of a 1450XLD (*) booting and/or in the self-test? Is there something extra for the 1450XLD? A test of the drive?
(*) Not a re-creation of the 1450XLD, but the real, original one...
I'd like to see it loading software on floppy (5x faster, right?), going in the self-test or going into BASIC...
 

[drac030]

37 minutes ago, ldelsarte said:

So, you turn on the computer and its built-in floppy drive at the same time. This is why the OS is modified to not display "BOOT ERROR" right away and wait for a floppy disk to be inserted.

I have compared 1450XLD OS-es (there are two versions) with 800XL OS some years ago and I do not remember any difference like that.

 

If I am not mistaken, 1450XLD drives are supposed to be PBI devices. Which mean that they have own ROMs activated by the OS as necessary (the same mechanism is used by Karin Maxi external floppy drive, or IDE+ HDD, or whatever else). The "necessary" time is e.g. OS initialization. The PBI ROMs get called one by one, so this would be the opportunity to check if the drive has finished initializations (and to wait, if it did not) and if there is a floppy inserted.

 

At least, that is my guess. Surely I would like to know how these drives work, how fast they are ("100 KB/s" mentioned in the sources probably means 100 kilobits/s) etc.

[+bob1200xl]

If I remember correctly, the system boots into PBI code that gives you the option of booting from the internal FDD or an external FDD as D1:.

 

Reading a standard diskette in the PBI drive is limited by the skew of the diskette. If it is a normal disk, it will read at the same speed as any drive.

 

You're better off running a SIO2SD with a modified OS.

 

100 kilobytes/s on the PBI, I think.

 

Bob

 

[+mytek]

Hi Bob

 

I think I recall reading somewhere that Atari was having problems with getting the XLD floppy drives to work properly. Did you hear something similar?

 

[+bob1200xl]

No. They seem to work OK. Maybe some kind of compatibility issue?

 

Bob

 

[+mytek]

1 hour ago, bob1200xl said:

No. They seem to work OK. Maybe some kind of compatibility issue?

If I come across what the issue supposedly was I'll post a link. But it very well could have been a compatibility problem of some sort.

 

[+kheller2]

There are two versions of the 1450XLD, the 1450 short board with a plug-in floppy board (and there might be two versions of that) and the long TONG board.  As I recall the boot methods and drive mechs varied.  There is a thread here somewhere discussing the drive types and also a boot method.  
 

short board early prototype floppies: 

a very different short board floppy board, original thread found:

 

TONG version device handler notes, pretty sure TONG used stock Shugart drives :

 

 

[drac030]

20 hours ago, bob1200xl said:

100 kilobytes/s on the PBI, I think.

Ok, so this means that one sector is transmitted at 100 kilobytes/s.

 

But 128 bytes per sector * 26 sectors per track = 3328 data bytes per track. 288 rotations per minute = 4.8 rotations per second. 3328 * 4.8 = 15974.4 bytes per second = 15.6 kilobytes/s maximum, with ideal sector skew.

 

If so, saying to the press that the disks work at 100 KB/s does not seem very fair.

 

[+bob1200xl]

I watched your video...

 

The keyboard is failing because the connector fingers have too much resistance. A key is 'pressed' when the path from the output of the key scanner to the input of the key multiplexer drop below a certain resistance. (something like 500 ohms - does not matter.) So, you need to add up all the resistance in any key circuit. Maybe 100 ohms for the key contact, less than 10 ohms for the printed wiring, and 50 ohms for the mylar connector to the PCB.

 

So, 150 ohms or so. Anything that adds resistance will bring the key closer to failure. It is always the PCB connector, even though it may seem localized to a few keys.

 

You have to realize that the system is not binary - contact or no contact... It is a scale with multiple components. You can screw around with the key contacts and such all you want, and it may seem like you're good, but fixing the connector works every time.

 

Bob

 

 

 

[ldelsarte]

Did you all notice the blue background (instead of green) in the "Memory test" & "Keyboard test" of the 1400XL?

Is it the same in the 1450XLD?

[+kheller2]

I did not, but that would imply this is a different OS ROM.  While there were several modifications to the XL OS during the 83-84 years, I don't remember the background being changed unless the V: T: Handlers did something. But I doubt that.

 

Keep in mind that the majority of "1400/1450" system/boards information you see floating around relate to the short board.  The 1400/1450 was killed then resurrected as a single board in early 84.  The floppy code was still being worked on in late August 84 for the 80C49 microcontroller and all sorts of new glue chips like Muffy.  It makes me wonder how many times Atari wrote code for stock double density (1053, 1450TONG) drives before the XF551.

[Faicuai]

On 8/21/2021 at 4:55 AM, ldelsarte said:

Did you all notice the blue background (instead of green) in the "Memory test" & "Keyboard test" of the 1400XL?

Is it the same in the 1450XLD?

XL OS-loads from Rev.2 onwards yield on darker-blue background in memory test (NTSC).

 

It should never be green, specifically on NTSC.