exxos's Atari, Amiga & retro forum

Sorry if this has been mentioned already, but I recently found out that FDC input pull-ups on the H5 are very weak. At least according to the schematics and expect for the RD signal, they are 10K, while the ST and the STE use 1K pull-ups. The signals are IP, WP & TR0. These signals transition at very low speed and the timing here is not critical at all, especially when the pull-ups determine only the timing for the non active raising edge. That means that they would probably work just with almost any pull-up resistor value. Nevertheless, the timing will be different.

Do we care about the timing of the trailing edge? There is anything that depends on that? I don't remember for sure, but there might be some copy protection that could break. But is the difference in timing produced by the weaker pull-up significant enough though? Probably not. But I thought I should mention the issue anyway.

I am in the process or commissioning an H5 for dev purposes :) so I’ll take a look at this when I get time and scope out. Will do a replace to a 1K to see the difference.

I suspect that Goteks are more forgiving or have their own pull-ups than an original floppy.

Hi Ikcy,

Icky wrote: 08 Feb 2023 06:53 I suspect that Goteks are more forgiving or have their own pull-ups than an original floppy.

The Gotek, I believe, does have its own 1K pull-ups. At least they are present in the publicly available Gotek schematics. In such case the 10K pull-ups at the computer are just fine. But not every drive has its own pull-ups at the output signals. The standard is that the pull-ups should be at the receiver side, the computer in this case.