exxos's Atari, Amiga & retro forum

I'm just looking at the floppy connector on the Falcon and it seems to be a little non-standard. Well, saying "non-standard" for floppy cables isn't really saying much, quite a few pins were used in different ways by different manufacturers. It's more trying to figure out what standard.

The pins which are a bit unusual are pins 2 & 6 (MODE_SEL_1 and MODE_SEL_2) and pins 29 & 33 (MEDIA_DET_2 and MEDIA_DET_1). I've found a reference for the newer higher desnity drives which use pins 2 & 6 to select the bitrate.

https://theretroweb.com/chip/documentat ... 180242.pdf

This seems to indicate that in general pin 2 is used in the conventional way for high density drives to select density (low for DD, high for HD) but then pin 6 can be used in conjunction with pin 2 to selected different bitrates for drives which support it.

Pins 29 & 33 are even less documented. It seems the Falcon was designed with the TEAC FD235J in mind with regard to extended desnity support. Or at least it looks like it can be configured to match the Falcon pinout.

https://hxc2001.com/download/datasheet/ ... d0010a.pdf

So pin 29 looks like it wants to be ED out (low = ED, high = HD/DD) and pin 33 HD out (low = HD / high = DD). So pins 29 & 33 are outputs from the drive indicating the type of media present.

I'm just putting this here partly so I've got it for reference, and partly so onyone else who might want to know this stuff has it in one place. It took quite a bit of searching to figure out what was going on. So it does look like the Falcon can support 2.88mb drives as stock.

But no drive B! Slightly curious they didn't route the DS1 signal from the PSG, they have a spare spot for it on the buffer used for DS0 and SS0, so why not route it? I mean, it was routed on the ST... and that is just as likely to have 2 drives connected to the internal floppy cable as the Falcon (and in fact I had two drives like this back when I had an ST).

Does anyone know if the Falcon requires HD detect on pin 33? I'm guessing it does to select the correct bitrate for AJAX, but I guess this could be done in software by trying one bitrate, then the higher and seeing if you get valid data back. Just wondering with physical drive replacement on the Falcon whether you need a more configurable drive (like the TEAC drives) or if you can get away with less configurable (like SONY).

To answer my own question, I just modified a Sony drive so it responded to DS0 and it can read only HD disks. So I think that makes sense. This Sony drive has no HD detect output (or input).

Looking at standard HD drives with HD detect output, though, like the TEAC FD-235HF, the HD detect output is on pin 2 and also appears to act as an input (so you can force HD on a DD disk but not vice versa). I don't have any TEAC drives at hand yo try, I'll have to order one.

But does this mean that the Falcon normally just uses pin 2 as an input for HD detect unless quad density is enabled via U47? In which case I assume it switches to using pins 29 & 33 as media detect input and pins 2 & 6 as the bitrate select output? I think that makes the most sense as if it was using pin 2 as output and software guessing then it should get it right eventually as it will by process of elimination hit the bitrate the drive is operating at based on the media.

Hmm, turns out I was wrong about the Sony drive not working with DD disks. My DD disks were just bad. I can't tell the difference in functionality between a TEAC drive with pin2 strapped as HDIN and the Sony drive which apparently does not have pin2 connected. So I'm not really sure what purpose the HDIN really serves to be honest.