Internal drive select

General discussions or ideas about hardware.
tzok
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Re: Internal drive select

Post by tzok » Tue Jan 19, 2021 12:45 pm

I'd be very surprised to find a drive, which would have a pull-up on drive select line higher than tens of kΩ. They are required to have one. I've tried another drive ("modern" HD drive - SFD-321B), and it required over 5mA to pull Drive Select to low, so a 1kΩ pull-up was there (again - no resistor on the PCB). It even measures this 1kΩ to +5V line, when powered off. Gotek also has a 1kΩ pull-up.

These FDD ICs are a kind of hybrid analog/digital chips. Many MCU, including popular ATMegas have internal pull-ups (sometimes switchable). There are many ways to produce a resistor on the IC die:
http://www.idc-online.com/technical_ref ... istors.pdf
It may be an active circuit, but also a passive one.

The specification says, that all host controller outputs should be open-collector, and all host controller inputs should have pull-up resistors. So any unconnected input on the drive side should be treated as inactive, and it is up to the drive electronics designer how he will cope with that.
I agree, that leaving an unconnected drive select line may be risky, but according to specification it should, and from what I verified empirically, it will work. I also think, that much better and simpler is to do this on the jumpers, instead of adding some extra ribbon cables or PCB adapters between the Atari and the FDD. This does not exclude adding additional pull-ups at the switch.

friijy2001
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Joined: Sun Jan 17, 2021 1:34 pm

Re: Internal drive select

Post by friijy2001 » Tue Jan 19, 2021 10:52 pm

Thank you for all your input, I may just use a pull up to be safe as I have some spare resistors from another project.

I’ll report back on how it goes!

friijy2001
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Re: Internal drive select

Post by friijy2001 » Tue Jan 26, 2021 7:29 am

Just in the process of building. everything seems to be going well although looking a little like frankenstein's monster lol!

With my understanding of the pinouts for the floppy drive pins 1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31 and 33 (all the odd numbers) are ground so I should be fine connecting these together and then joining one connection to the gotek and floppy?

As per the previous diagram:
  • I will connect pin 10 and 16 to a DPDT switch (10 with a pull up) on the gotek and main floppy
  • Pins 2,4,6,8,12,14,18,20,22,24,26,28,30,32,34 with the corresponding pins on the floppy and gotek.
Hope that make sense and if someone can just check my sanity on the ground pins :)

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exxos
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Re: Internal drive select

Post by exxos » Tue Jan 26, 2021 9:03 am

Yeah all gnds are connected together ... Which is all the row on the connector.
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friijy2001
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Re: Internal drive select

Post by friijy2001 » Tue Jan 26, 2021 12:34 pm

Finished the main breadboard and connectors and tested it today.

At first both drives powered up but the ST could read the drives. As a further test I disconnected the power from each drive and they both worked when I flicked the rocker switch from the gotek to the internal floppy! It’s alive!

So in conclusion i will have to use two switches one to switch the pin 10 and 16 from the gotek and floppy and another switch to switch the 5v power from the gotek to the floppy.

I’ll do some more work and report back if it works :)

Once this is done its just installing everything neatly inside the ST so I can just with a flick of a switch decide which drive A to use.

(The reason I did it this way is I did not want to mess around with the main circuit board or Yamaha chip and wanted something I could plug in using IDC cables, switch across and it was nice a neat inside the case) if I want to buy a B drive it keeps the din port free too.

tzok
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Re: Internal drive select

Post by tzok » Tue Jan 26, 2021 3:07 pm

friijy2001 wrote:
Tue Jan 26, 2021 12:34 pm
So in conclusion i will have to use two switches one to switch the pin 10 and 16 from the gotek and floppy and another switch to switch the 5v power from the gotek to the floppy.
Unless you have incorrectly set jumpers, Gotek has pin 16 not connected to anything... switching PIN 10 hast to be sufficient, you are doing something wrong if it doesn't work.

To make a simple test, leave both drives connected (on a straight floppy cable), just remove ALL jumpers from GOTEK and the internal foppy should work. Then remove a DS0 jumper from internal floppy, and put DS0 jumper on GOTEK - now GOTEK should work. Don't use any additional boards, just a straight floppy ribbon, with 3 IDC connectors.

friijy2001
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Re: Internal drive select

Post by friijy2001 » Tue Jan 26, 2021 4:27 pm

I’ll give the jumper option a try, the above worked perfectly though and stopped the whirling of the floppy when I was using the gotek too.

Luckily I have plenty of room as it’s an STFM model so the gap between the PSU and floppy is ample to fit this in :)

tzok
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Re: Internal drive select

Post by tzok » Tue Jan 26, 2021 7:33 pm

If you want to avoid running a motor in FDD, you indeed need to break the pin 16 to the FDD, when Gotek is selected. However, if you have a standard 2 drive setup, motors in both drives also work simultaneously.

friijy2001
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Re: Internal drive select

Post by friijy2001 » Fri Jan 29, 2021 8:44 am

ok all in and working...sort of!

Having a very strange thing happen, so a little stumped, i'll explain :)

I have both drives connected with a switch for pins 10 and 16 as mentioned, drive jumpers are in place and have both drives connected. When I flick the switch it switches from the gotek to the floppy (both as A drives), it loads games fab!

However...
If I use the HXC software for the gotek ( viewtopic.php?f=12&t=593&start=10#p4174 ) and allocate a game/application to slot 1 or any slot and press F10 to save and reboot it does not save the config. If I disconnect the ribbon and do the same as above it saves to the required slot and reboots and plays.

As a further test I created a blank image on the gotek, went to the desktop and saved the desktop config, with the ribbon connected to the floppy drive it said it cannot save due to write protect but with the ribbon disconnected it saved the desktop config to the gotek blank disc.

Am thinking it's the write protect pin on the floppy that is causing this, as I have a spare terminal on the switch I was going to have an on/off on pin 28?

So when the gotek is selected it cuts the pin 28 on the floppy.

Would be interested in hearing your thoughts

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Re: Internal drive select

Post by exxos » Fri Jan 29, 2021 12:08 pm

I understand the logic.. but that would mean drive B: could never work.. Once DS is high / disabled, the drive should be ignored.. But I also assume you are not switching drives with the power on ? As that probably wont work as you would have to press ESC to refresh the drive before saving to it, else TOS will have the previous FAT data form the previous read floppy.. hence corruption..
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