ATARI floppy disk drive XF551, 2_3.

By Administrator at August 16, 2010 01:13
Filed Under: Atari

Prerábka stanice XF551 na 720 kb (používa floppy disk 3.5")

(Modification XF551 for 3.5" FD)

Predstava XF-ky s mechanikou 3.5" je hodne lákavá, takže poďme na to !





Autorom prerábky je Bob Wooley a popis tejto zmeny nasleduje:

Inside the XF551 Disk Drive by Bob Woolley (SLCC)

It has been almost a year since I first got my hands on an XF551. Busy little hands... Of course, the first thing I did was to tear the thing apart to see how it was put together. And, maybe do a little "put"ing myself. As a result, I have made a few modifications that may be of interest to other XF551 owners. You will not be able to successfully make these changes unless you have reasonably decent electronic skills, so don't gamble with your new XF551 unless you know what you are doing. Most User Groups have skilled members that will be happy to guide you if you need help.


But, before I get caught up in details of the drive, I would like to clarify some points on the XF551. The drive IS double sided and can read and write in single, enhanced or double density. The "book" that comes with the drive is incorrect. MyDOS, SuperDOS and SpartaDOS canall format the drive as double sided and double density. Previous Atari drives did not use the INDEX hole on the diskette, which allowed us to flip the disk over and format the back of the media. The XF551 uses a standard, bone stock, IBM-style drive. It uses INDEX. It will not FORMAT the back of a diskette unless the disk jacket has two index holes. It WILL read and write to the back of any disk. Guaranteed! On side one, the tracks on the disk are written from the outer edge in, from 0 to 39. On side two, the tracks are written from the inner edge out. This allows us to read the first 40 tracks of a DSDD diskette on a SSDD drive. The second side is not backwards nor could it be read on a SS drive even if you changed it. The speed of the drive is NOT 288 RPM, the speed you are used to seeing, but 300 RPM, the industry standard. The XF551 compensates for the difference by using a clock frequency 4% (.33mhz) higher than it should be. This will read and write the data in exactly the same place on the diskette as your 288 RPM drive, although programs that measure the speed of the drive will read 300 RPM.

Talking To The Drive

The XF551, as it comes from Atari, has the ability to format a diskette in any of three configurations: single density (SSSD-88K), 1050 density (SSED-127K) and double-sided, double density (DSDD-360K). The DSDD format has a standard skew (skew is the physical sequence of the sectors on the disk) and a high speed skew option available to the user. This extra skew layout allows faster data transfers on the SIO buss, much like the ICD Doubler upgrade on the 1050. For those of you interested in programming, the DSDD format SIO command is $23. For a high speed skew format in DSDD, you just need to turn on bit 7 for a value of $A3 (the SSSD and SSED formats do not have a high speed skew, although the drive will transfer data at high speed in those densities). To transmit data at high speed to and from the XF551, just set bit 7 of the command to "1" again (a get sector ($52) with bit 7 on is $D2). You must still send the command frame at the normal SIO rate ($28 in $D204) and then set $D204 to $10 for high speed operation during the data frame. The drive will also recognize the Put (and Get) Option Table command ($4F and $4E), which are similar to the Percom configuration table operations. Only bytes 4-8 are changed by the Put command, however, and only the three supported formats will be recognized. Even if you sent the Option Table a 512 byte sector size, you would only get 256 byte sectors. A number of the newest DOS versions (SpartaDOSX, SuperDOS 5.0, DOSXE...)now have XF551 support built in. Also, a file is available in Atari8 on CompuServe that will modify SpartaDOS 3.2D for the XF551 features (in DL3 - XF32D.BAS). Using any of these methods will transfer data almost twice as fast as DOS 2.0.

Into The Hardware.

The first thing you notice about the ICs in the drive is the one in a nice socket, the ROM. Makes it a lot easier to burn an EPROM (use a 2764) to make code change if you can just plug and unplug your devices. I didn't see the ROM source code printed anywhere, so I wrote a simple disassembler for the 8050 MPU used as the brains of the drive. [Some were manufactured with an 8040. It has the same 256 bytes working RAM as the 8050, but no built-in ROM. Apparently the internal ROM was never used, as the drive OS is on its own ROM elsewhere on the board. - L.S.] It was very nice when Atari used a 6507 (which uses 6502 OPCodes) in their drives but, no more. Everything Atari comes out with now seems to use a different chip and this 8050 stuff was a bear.
Finally, I got most of the program logic worked out and designed some changes:
One upgrade that was available for the 1050 is a ROM change that will re-address the drive as D5: through D8:. This can be done on the XF551 ROM by altering location $0095 from $31 to $35 ($33 gives you a range of D3: to D6:, etc.). Having 360K is nice. Having 720K is even nicer. Putting a 720K, 3.5 inch drive in place of the stock drive is not too hard, so let's start with the ROM. There is a little bug in the code that allows the drive to start writing the track before it has reached operating speed. To remedy that, change $528 from $90 to $00, $C1D from $88 to $80 and $E25 from $88 to $80. [I have heard reports that this may be unnecessary, so you may or may not want to make the aforementined changes. I have had the problem, so better safe than sorry. - L.S.]
The 720K drive has 80 tracks per side which requires you to change $680 from $28 to $50, $80F from $30 to $60 and $811 from $FD to $FA. A 3.5 inch drive uses a 3ms seek time -- change $53D from $00 to $03, $57B from $18 to $13, $9D1 from $08 to $03, and $B15 from $18 to $13. Finally, the 3.5s use write pre-compensation -- change $61D from $F6 to $F4, $621 from $F6 to $F4 and $D0D from $A2 to $A0. For a drive, I used a unit from JDR Microdevices (MF353B Mitsubishi) that plugs right into the 5.25 connectors and uses the same mountings as the larger drive. This simplifies the installation quite a bit. When you go to plug in the 3.5, you may notice that the 34 pin cable is too short. I de-soldered the connector and added a longer cable, but one hacker, Joe Wyks, managed to pry the top off of the board connector and crimp his new cable into place without soldering. [The latter was the method I used, as it is a little easier on the circuit board. L.S.] The power connector can be adapted with cables made for that purpose, if necessary. That's about all that's needed to run a 720K 3.5. Format a disk using SpartaDOS XINIT, option 7 (DS 80 tracks) and start filling it up! You now have 2880 DD sectors.


Upravené obsahy EPROM pre 3.5" FDD:

EPROM for 3.5"


Vhodné 720k disketové jednotky:

Tieto mechaniky 3.5" určite fungujú:

3240-U TEAC TEAC FD235HF FD235HF 5165-U TEAC FD235HF 6291-U

Mitsubishi MF353 B Epson SMD-300 a (interná / externá) Amiga Floppy:




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XF551 1_3

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XF551 3_3


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8/17/2018 10:02:32 PM #


ATARI floppy disk drive XF551, 3_3.

ATARI floppy disk drive XF551, 3_3.

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Volám sa Igor Gramblička, bydlisko: Bratislava, Slovakia. Môj nick: Igi. Blog je o mojich záujmoch, predtým som pracoval ako IT špecialista na počítačové siete a redakčné systémy pre viaceré denníky - až som pred rokmi nakoniec v jednom z nich zakotvil a kde som to potiahol až do konca mojej profesnej kariéry.

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