Mega STe 1.44 floppy behaviour and 1772/AJAX

[Pacman]

I've put a Sony 1.44 MB (MPF 520-1) inside my Mega STe along with the needed GAL chip and single wire connection between it and the CPU.
As I've had problems with the computer for a while (just repaired!) I haven't had a chance to properly test the setup, but it appears to work fine with HD floppies.

I have a WD 1772-02-02 in the MSTE and understand it's the best way to go if you don't have an Atari AJAX chip. Apparently the 02-02 should handle 16 MHz (HD mode) as long as it's not continous, right?
For normal ST computers, most HD modules (like the ones by Exxos) don't feed 16 MHz into the 1772 unless needed, but I was curious about the MSTE as there hasn't been much information about how it handles HD floppies.

So, using a digital multimeter I checked pin 18 (clock of the 1772 (datasheet with pinouts) and quickly found out that when a HD floppy was inserted and read it (obviously) switched over to 16 MHz, but surprisingly it stayed that way after the drive stopped spinning and even after ejecting the floppy disk.
It was only after inserting a DD disk that it returned (and stayed at) 8 MHz. So it appears that the clock frequency depends on what kind of floppy you had inserted when first accessing the drive. I haven't done any extensive testing yet (I should probably see what happens when I boot the computer, and without a floppy inserted), but is this the way it works in an MSTE?

I should probably also check how I've modified the drive itself -if I've done it in the same way as with a normal ST or not. Anyone who knows more about all this with the MSTE?

[troed]

Yes. TOS tries to read the FAT and if it doesn't get sane results back it switches frequency. It _does not_ detect disk type from the drive signal.

/Troed

[exxos]

I think @troed looked into it a while ago, I think the 02-02 fails after a few hours run time at 16Mhz as it doesn't downclock to 8Mhz like my 1.44 kits do.

[rubber_jonnie]

Out of curiosity what revision mainboard do you have? If it's B or later then the jumper wire between the GAL (PAL) and the CPU isn't required according to the 1.44MB upgrade manual from Atari.

Don't know what effect it would have if connected and not needed but maybe worth a check. Docs can be found here: https://docs.dev-docs.org/

[Pacman]

Out of curiosity what revision mainboard do you have? If it's B or later then the jumper wire between the GAL (PAL) and the CPU isn't required according to the 1.44MB upgrade manual from Atari.

Don't know what effect it would have if connected and not needed but maybe worth a check. Docs can be found here: https://docs.dev-docs.org/

I'm not sure if it's a "B" or later as I can read both "Rev 4.1" and "B-VO" as well:

mste_mainboard4_1.jpg

It's certainly worthwhile looking into all aspects of this as maybe the wire makes a difference.

I think @troed looked into it a while ago, I think the 02-02 fails after a few hours run time at 16Mhz as it doesn't downclock to 8Mhz like my 1.44 kits do.

I'll try the forum's search and see.
When you say "fails after a few hours" -do you mean permanently, or will it work again after a while of powering down?
I suppose if only use DD disks or have no disk inserted into the drive it'll stay at 8 MHz all the time?

Yes. TOS tries to read the FAT and if it doesn't get sane results back it switches frequency. It _does not_ detect disk type from the drive signal.

So it really works in a lot simpler way than in a normal ST with a HD module?
Does this also mean that in a MSTE you don't need the usual Atari drive modifications (shorting the "CTIN" switch, adding a wire between the "HDIN" switch and pin 2 of the drive's data connector), and can just insert any PC type HD floppy drive (possibly needing to change DS1 to DS0)?

[frank.lukas]

Atari Mega STE, Atari TT and Falcon need a normal unmodified PC Type Floppy Drive only set to DS0 ...

Also you need a AJAX Controller. I have some faulty 1772 there work with 16Mhz some time.

[troed]

When you say "fails after a few hours" -do you mean permanently, or will it work again after a while of powering down?

It overheats and starts to fail reading disks. At least that's the symptom in my MegaSTE with a 02-02 that otherwise works with a "regular" ST HD mod.

/Troed

[troed]

Here's what exxos alluded to - my investigation into this a few years back:

https://blog.troed.se/2017/01/20/the-ta ... i-mystery/

/Troed

[exxos]

When you say "fails after a few hours" -do you mean permanently, or will it work again after a while of powering down?
I suppose if only use DD disks or have no disk inserted into the drive it'll stay at 8 MHz all the time?

If you run at 1.44mode some hours the chip will start overheating and start to malfunction, if you let it cool down it will likely still work perfectly fine... If you were running 720K mode all the time, then there should be no problems AFAIK.

[rubber_jonnie]

Just going back to the official upgrade docs, and as has been mentioned, this upgrade does specifically call for an Ajax.