MEDIA CHANGE FIXS

Update your old 720k to a 1.44 drive etc.
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exxos
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MEDIA CHANGE FIXS

Post by exxos » Mon Dec 18, 2017 11:40 am

As there is no easy tested solution for this I just created this solution which seems to work. It is basically the same mod as I use in my V6 floppy upgrade kit. But in this case the mod is done internally in the GAL.

This mod could likely be done with the logic level MOSFET in which case it would not need the resistor. But I do not have any these at the time of typing and well.. Life is too short :lol:

In any case I use a simple PNP BC558 transistor. Any generic low-power PNP transistor will likely work.

PNP transistor...
connect:

C to 0v (WD pin 14)
B via 1K to MON (pin 20)
E to WP (pin 25)

When MON is high, transistor is off.. When MON is low, transistor turns on, connects WP to 0v. In this case TOS should always assume that disc has changed and should always re-read the FAT.

MCFIX.jpg
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The program to use is here..
http://www.exxoshost.co.uk/atari/last/floppy/MEDIAC.TOS

This program was just a very fast knock up in STOS a few years ago.. But does the job.

If run on a unmodded ST the message will say "Disc has definitely not been changed" constantly.

On a modded ST. After loading and the floppy drive light turns off, the 558 will set WP LO and the message will say "Disc may have changed!". The message shows up regardless of if you actually change the floppy or not.

I have only done some quick tests with this is to work okay obviously others need to try this as well..
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: MEDIA CHANGE FIX

Post by exxos » Mon Dec 18, 2017 6:51 pm

Further to a discussion here

I did a quick test to a MPF920 drive as these seem to have a third switch which I use.. Which I assume is media detect switch..

mf9201.jpg
mf9201.jpg (344.31 KiB) Viewed 569 times
mf9202.jpg
mf9202.jpg (169.77 KiB) Viewed 569 times

What this does is that when the floppy is ejected, the media switch becomes open circuit and is pulled up to 5 V via a 1K resistor on the motherboard. This then turns on the BC548 NPN transistor which connects WP to 0V.

So with this modification TOS only informed of a disc change when the disc is physically ejected..

This mimics the behaviour of the Epson 480 drive which I tested. However the Epson drive only pulses WP low, My fix keeps WP low all the time until the disc is inserted. I do not really see there being any difference to either method... But obviously this mod should be tried by others also..

I am also actually assuming this switch which I am calling media detect switch, is actually media detect switch.. There could be other switches use with 2.88MB floppies, but in the case of this drive it doesn't seem to be near any holes for any floppy types..
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

Bikerbob
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Re: MEDIA CHANGE FIXS

Post by Bikerbob » Mon Dec 18, 2017 9:11 pm

OK, I will do this one first then. I think this is in effect what the Alison wire was doing.. the positions look the same. But I also have an NPN transistor I can use, so I will do your mod and confirm. :)

James

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Re: MEDIA CHANGE FIXS

Post by exxos » Tue Dec 19, 2017 11:47 am

Bikerbob wrote:
Mon Dec 18, 2017 9:11 pm
OK, I will do this one first then. I think this is in effect what the Alison wire was doing.. the positions look the same. But I also have an NPN transistor I can use, so I will do your mod and confirm. :)
I don't know what Alison was doing, but this mod cannot be done to simple wire.. Transistor is being used as a inverter... As when there is no floppy inserted, which contacts break, and once which pin is pulled to 5 V.. We need to switch WP to 0V.. So obviously we need inversion here... And the transistor also acts as tri-state buffer.. In that when the switch is closed, the transistor is turned off and does not affect the WP signal.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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