4.10 AJAX

AJAX Floppycontroller

Zum verbesserten "AJAX-Chip" gibt es nicht viel zu sagen, ausser das er zum Betrieb eines HD-Diskettenlaufwerks nÜtig ist und das er deutlich teuerer ist, falls ¦berhaupt erhèltlich, als ein normaler WD1772.

Entsprechende HD-Module und deren Beschreibung finden sich hier in der FAQ.

Ein åbertakten des normalen Floppycontrollers ist vom Prinzip her nicht anzuraten da man sich auf die geschriebenen Daten ja gerne verlassen mÜchte. Es ist also immer besser einen AJAX-Controller zu verwenden.

Der AJAX-Chip trègt die Bezeichnung: C302096-001A (Toshiba) oder C302434-001A wenn er von (National) stammt. Beide sind exakt gleich. Auf dem Chip selbst steht auch Ajax oder Atari drauf.

Diese Controller kÜnnen in jedem beliebigen ST/e, TT, und Falcon verwenden. Der Falcon hat den AJAX bereits ab Werk eingebaut.

The WD1772 drive controller will not reliably support the high density floppy drive. You'll need to change it to the newer AJAX controller.

The AJAX chip number is C302434-001/A.

WD1772-PH
02-20 9035

Well, the original WD1772 was tested at 8 MHz. Some of them would do 16 MHz, but were not tested for that. The WD1772-02, howeever marked, does the 16 MHz necessary for a HD drive.

As far as I know, the suffixes on WD1772 refer, in fact, to the temperature range that the chip is certified for. Thus, WD1772-02-02 has a wider temperature range than WD1772-00-00, and can better withstand heating caused by overclocking. So far i know the details of TT schematics use the WD1772 chip in the same way as ST/Mega i.e. switches its clock from 8 to 16MHz for HD floppie support.

It is well known that a ST or a MegaST one has to install a small electronic circuit to do this switching. All the variants of this that I have seen are made so that the chip is fed by 16MHz MOST OF THE TIME- except when there is a DD floppy inserted. The overheating problem is thus understandable.

But this small circuit can be made so that it switches the WD1772 to 16MHz ONLY when the floppy is working (i.e. its motor spin up) AND a HD floppy disc is inserted. In this way the chip is subjected to 16MHz only for brief intervals when the floppy is actually used, and the overheating would be much less. I suspect that a WD1772 even with a lower temperature rating might do the job then- but I didn't try that.

I have installed a circuit with this additional capability in my MegaST (a little board with a single 74LS151 chip, sitting piggyback on the WD1772). Admittedly, this is WD1772-02-02, but anyway, it has been working for a couple of years now with HD floppies, without a single problem.

The AJAX chip does exactly same thing as the WD1772-02, and costs a lot more!

I believe the C302096-001A was the original AJAX that Atari used in early model TT030 systems. It was later replaced with the C302434-001A. They may very well both be identical except from different mfrs., but I can't confirm that for sure (nobody left to call at Atari).

C302434-001A = Ajax National
C302096-001A = Ajax Toshiba

By the way, the "AJAX" (anyone know why it goes by this name or what it stands for?) can handle up to 32 MHz, which is what ED (Extended density, 2.88Mb disk drives use). The Western Digital WD-1772 can only handle 8 MHz (720 Kb) as mentioned several times already here, but if anyone wants to take the chance and perhaps fry the chip, go ahead and use it with 16MHz. Personally I'd stick with the AJAX than to risk not being able to use my disk drive at all because I don't have a spare 1772 in case something goes wrong.