DPF-550 Floppy drive

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By mohai

Paladin (892)

mohai's picture

11-01-2011, 20:16

Hello,

i am dealing with a disk interface branded AVT. Model is DPF-550.
It is manufactured by Daewoo. Indeed, it is the same model as Daewoo one.
There are other similar branded like Talent, ECC or Dynadata.

It has a 5,1/4 drive as de-facto, single sided and simple density (SS,SD, 180K) and a connector for an external drive (34 pin, but reversed pins, by the way).

After some tests, i was able to change internal drive with a 3,1/2 one and i got 360K. I am able to format discs and work with them, too.
Using a PC with MS-DOS, i can work with these disks with no problem.

The problem is that i do not know which densitiy it is using or if two sides are used.
I tried with regular DS DD / SS DD (720 and 360 K) but reading is not good.
If i try to read a couple of times (reading forced), then i am able to see files in directory but
nothing loads. I always have error messages.

Controller chip used can handle double density (WD1770) and pin to select density is connected to some other
chips, so i think that firmware can control type of disk and driver.

Now, the question is: Does anybody knows of a compatible model that can handle 720K and 360K regular disks?
Maybe a ROM change can help? Any compatible model?

By the way, disks are signed as DWDPF510. This make me think that ROM is from another model and does not
make use of all features in this drive.

NOTA: External drive can be A: or B:, but al handle disks the same way as internal one

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By Manuel

Ascended (17048)

Manuel's picture

11-01-2011, 23:03

I'd expect it to be SS DD. Sounds like the drive is not OK, something with head alignment or worn out drive belt?

By flyguille

Prophet (3028)

flyguille's picture

11-01-2011, 23:24

i have one, but branded Talent, and did exactly what you Did, I hook up a 3 1/2 drive in the (reversed external connector)

The controller /driver /msx did believe that your 3 1/2 is an 5 1/4 drive.

so, when it formats, it does like a 5 1/4 disk drive, so each track is less compressed & with less sectors thant real 3 1/2. the drive will spin fastar, but as you are reading at the same speed that you recorded it, is all ok.

also the bootsector ID/FAT12 will be of a 5 1/4 disk, so any soft that reads IDs will believe that it is a 5 1/4 media.

you do not needs any change in the firmware/controller/drive. But do not expect to obtain 720K disks because that controller-chip is only DD (double density).

For get a good & reliable experience, when you use HD (1.44MB disks) and a drive of 1.44MB (PC Drive) just fill the hole of the disks to tell to the drive that it is a 720K media, so each track will be WIIIIIDERRR and you will avoid the loss of data.

also bad disks like every disk manufactured in this century sucks.... nobody can tell you why every brand lowered a lot the quality of the media and its life-safe-period. (like bringing the disk from work to home, and it turns in a buggy disk!).

I also found that inserting the disk in a 3 1/2 drive at a PC, the PC can read the disk (atleast win98 era), but do not write (insert always with the read-only protection on).

By flyguille

Prophet (3028)

flyguille's picture

12-01-2011, 00:35

PD: If I remember correctly, in PC you needs to set 5 1/4 option, for your 3 1/2.

By mohai

Paladin (892)

mohai's picture

12-01-2011, 09:40

i have one, but branded Talent, and did exactly what you Did, I hook up a 3 1/2 drive in the (reversed external connector)
The controller /driver /msx did believe that your 3 1/2 is an 5 1/4 drive.
so, when it formats, it does like a 5 1/4 disk drive, so each track is less compressed & with less sectors thant real 3 1/2. the drive will spin fastar, but as you are reading at the same speed that you recorded it, is all ok.
also the bootsector ID/FAT12 will be of a 5 1/4 disk, so any soft that reads IDs will believe that it is a 5 1/4 media.

That is correct!
Yesterday, i checked bootsector and it seems that interface is fixed to 5,1/4, SS, SD. Media type is 0xFC, only one side and 360 sectors !!!


you do not needs any change in the firmware/controller/drive. But do not expect to obtain 720K disks because that controller-chip is only DD (double density).

I am afraid that controller-chip is SS and DD capable en.wikipedia.org/wiki/Western_Digital_FD1771.
It is strange that density select pin is not forced to SS nor DD. Also, all drive signals are available in both connectors but some are not used (like Head Select).
It seems that Daewoo put an outdated firmware in it.

I also found that inserting the disk in a 3 1/2 drive at a PC, the PC can read the disk (atleast win98 era), but do not write (insert always with the read-only protection on).
That was not my problem. I was able to read and write from PC using MS-DOS (Win 98) boot disk with no problem.

But now main problem is to read "regular" disks from other MSXs.

By flyguille

Prophet (3028)

flyguille's picture

12-01-2011, 18:14

you can to download here at MRC my draw of the circuit-scheme of the PCB that in the case of the Talent brand is configured for double side, the draw I did when I dissasembled my PDF-550 hardware as I did with the firmware.

if you want, I can to send to you the ROM image that handles & format 360K disks (40 tracks per side/ double-side)

the WD177x , has nothing to do WITH SIDE selection, the side selection is done by a bit of the register mapped at 7FBC / BFBC, it is three functions, MOTOR ON plus DRIVE select, plus SIDE select (iirc the side select is at bit 0).

This register is rendered by a regular TTL chip, so it is easy to hack/upgrade.

IIRC, it is bit0 = side select (0= upside)
bit 1 = select drive 1
bit 2 = select drive 2
bit 3 = motor ON.

(both drives spins at the same time).

the "drive select" only turn on the HEAD R/W electronics at drives. So the WD chip only receives the RAW data of the drive that is selected. If not selected the electronics turn off so it acts as a MUTE.

What controls if it is double side is the firmware + that TTL... WD chip has nothing to DO.

By flyguille

Prophet (3028)

flyguille's picture

12-01-2011, 18:21

PD: reading regular 720K disks of others MSX is not possible with that WD controller. For that you needs to upgrade to wDx97x or was the WDx79x family.... never mind.

By mohai

Paladin (892)

mohai's picture

13-01-2011, 21:14

Flyguille,

you are right.
Controller chip is capable of double density, but side select pin is managed by other chip (connected to some bit in some port ...).

I found a Microsol ROM that can be suitable. I will make some tests an post results.

Regarding diagrams, i cannot find them in MSX.ORG. Can you send me a link?

By flyguille

Prophet (3028)

flyguille's picture

13-01-2011, 21:28

I found something better, the original daewo scheme draw.

http://3.bp.blogspot.com/_lGdEZweweRo/S9EbwfPKEJI/AAAAAAAAALE/6xnmJei8qcI/s1600/dpf550sche.jpg

and here is the datasheet of WD chip

http://www.datasheetarchive.com/WD1772-datasheet.html

I found that you are right, D3 at 7fbc is controlling the switching DDEN of WD (FM vs MFM compression aka SD vs DD).

But I do not remember that in my Talent model, maybe in my talent model it is fixed to DD. & D3 controls Motor ON.

IC8 is the holder of the 7fbc / bfbc register WRITE ONLY register.

By flyguille

Prophet (3028)

flyguille's picture

13-01-2011, 22:20

I will explain a bit the circuit.

All registers including WD chip is mapped at 7fb8 up to 7fbC (page 1) (but it is bit 14/15 regardless) so, for a point of view of Z80 it is doubled also on bfb8 up to bfbc (page 2) (as it uses the msx-slot signal that mixes SLTSEL plus page1/2, it does not appears in page 0 and 3).

Now, this board supports the switching of ROM but only one is used anyway. How to switchs rom, just accessing to 7fbE or 7fbf one is one ROM other is the other ROM (that is a empty socket)., just ACCESS, you can read that adress and that will make it.

WD chip is at 7fb8 up to 7fbb, 7fbc is that IC8 TTL.

so, in the circuit you will found FIRST an address decoder, for hitting the xfb8 xfbf RANGE. THIS IS IC5.

at its output is the switcher that makes the selection of ROM to use, and the ENABLE for using WD chip or ROM or the TLL IC8, you has a JUMPER to select the DEFAULT rom.

You has a flipflop to hold the status of the ROM switcher it is below the IC5.

.....

at 7fbc = (according to diagram) , bit 0 = drive sel 0 , bit 1 = drive sel 1, bit 2 = side select, bit 3 = density select.

but it is the original daewo model.

Smile

By RetroTechie

Paragon (1563)

RetroTechie's picture

14-01-2011, 15:27

PD: reading regular 720K disks of others MSX is not possible with that WD controller. For that you needs to upgrade to wDx97x or was the WDx79x family.... never mind.
IIRC the Deawoo CPC-400S also has a WD1770 (or 1772) controller, and has built-in 3,5" DD drive (DS too I think).

With 279x you have an external Xtal frequency with multiple of data transfer speed, and a hardware pin that can do frequency /2. And perhaps a register bit too for this purpose? (not sure about that). Of course this is meant to switch between SD and DD easily. So for same data rate, you may have some Xtal frequency, and hardware pin set to 'no /2', or double that Xtal frequency, and hardware pin set to '/2'. Maybe WD1770 has similar combined method to set the transfer rate?

If that's the issue, I suggest you check datasheet/crystal/hardware pin, and compare with other machine(s) that have same controller, but the desired density as standard.

Then there's the logical format: with 5,25" disks you may have 360K by using 2 sides with 40 tracks per side. With 3,5" you have 360K using 1 side with 80 tracks. Maybe that's the problem with those disks you could list directory but not read files from? This might require a diskROM change, so that recognised media descriptors, # of tracks/sides etc. all match up. If you can dig up source code for the diskROM you have, there's a table in there somewhere with the media descriptors it recognises, and what parameters it uses for each one.

For get a good & reliable experience, when you use HD (1.44MB disks) and a drive of 1.44MB (PC Drive) just fill the hole of the disks to tell to the drive that it is a 720K media, so each track will be WIIIIIDERRR and you will avoid the loss of data.
Ehm... between 3,5" DD and HD disks, the only difference is the data transfer rate, combined with magnetic material used on the disks. Number of tracks, track width & rotation speed is the same. And it's possible to use HD disks in DD floppy drive (or HD drive thinking that DD disk is used), but then recording is very unreliable as practice has shown - count on those disks becoming unreadable soon... Evil

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