H4 1.44mb modification

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kodak80
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H4 1.44mb modification

Post by kodak80 »

For this modification, you will need a programmed GAL22V10 IC or you will need to request the code from Exxos or Icky. This is for the H4 builders only and not to be shared. As the code is not freely available, I would recommend that anyone programming the GAL ICs should set the protection bit to stop them being re-read and copied. The speed of the GAL doesn’t matter but I used GAL22V10D-15LP chips for my testing. I believe GAL22V10C or GAL22V10B or similar will work as well.

Once you have the IC it needs to be inserted into IC12 on the H4 board. The 1.44mb IC will not be active until you set JP22 to pins 2 and 3.

Ensure that the 16mhz Oscillator is on the H4 board - you need this for the 16mhz feed to the 1.44mb IC to work with 1.44mb floppies. The 1.44mb IC outputs 8mhz and 16mhz clock signals to the WD1772 IC through pins 2 and 3 on JP22 based on the voltages received from JP18 and JP19.

Overview of the components involved in getting the 1.44mb modification working:
1.44 Floppy Mod - components.jpg
1.44 Floppy Mod - components.jpg (62.44 KiB) Viewed 6523 times
Key
  • JP18 = Drive 0 with IC12 in use - Shorted means 720K floppy in use, open means 1.44mb floppy in use
  • JP19 = Drive 1 with IC12 in use - Shorted means 720K floppy in use, open means 1.44mb floppy in use
  • JP22 = WD1772 clock input control, pins 1 and 2 shorted means fixed 8mhz clock, pins 2 and 3 shorted 1.44mb IC controls clock
So for the 1.44mb mod to work, you need JP22 with pins 2 and 3 connected. JP18 and JP19 can be set open or closed based on the floppy disk you want to use. If you do not need to switch between 720kb and 1.44mb then you can leave these jumpers set.

Floppy drive or Gotek (with FlashFloppy):
Now to automate the JP18 input so that you can use both 720k and 1.44 floppy disks as they are mounted/used.

You will need a 1.44mb floppy drive or Gotek. The H4 should work with drives set with SEL0 or SEL1 unlike he original Atari boards this is an improvement as you no longer need to change the floppy drive solder jumper.

Here is what I have that works with my Gotek drive:
IMG_4501s.jpg
IMG_4501s.jpg (234.1 KiB) Viewed 6523 times
JP18 bottom pin is connected via the brown cable to my Gotek drive pin 2. Gotek pin 2 then sends 5v (1.44mb) or 0v (720kb) based on the floppy image mounted in the Gotek.
JP19 is shorted which would set drive 1 for 720kb use.
JP22 has pins 2 and 3 connected so that the 1.44mb IC controls the clock speed to the WD1772. The 1.44mb IC only sends the 16mhz clock when the floppy is accessed. When a 1.44mb floppy is not accessed then the signal returns to 8mhz. For 720kb disks the clock is set to 8mhz for access.

FlashFloppy configuration
I have v2.14 FlashFloppy firmware in my Gotek but I am not sure if you need the latest version for the pin 2 setting to function.

First, reset your Gotek drive FlashFloppy configuration by removing the USB stick and holding both buttons for 3 seconds. The OLED should display the reset to defaults message. I would guess the 7 segment display would also show an indicator that the configuration has been reset. This then allows you to reload the configuration from the USB stick FF.CFG when inserted.

For the FlashFloppy firmware to control the voltage on pin 2, you need to have the following in your FF.CFG file:

interface = shugart
pin02 = ndens


FF.CFG should be in the root of your USB stick or if you have a FF folder on the stick then the file should be in this folder.

You probably don’t need to set the interface setting as the default would probably work as auto but I have only tested with both the above options set.

Hopefully this information is clear. If not let me know.
Atari Falcon 030 | Atari 1040 STE | Atari 1040 STFM | Atari 1040 STF | Kryoflux & Supercard Pro Flux boards
Creator of the Atari ST Review magazine archive: https://www.chillichai.com/atari-st-review
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Icky
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Re: H4 1.44mb modification

Post by Icky »

:goodpost: - Nice guide @kodak80
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DoG
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Re: H4 1.44mb modification

Post by DoG »

pm sent to @Icky
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Icky
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Re: H4 1.44mb modification

Post by Icky »

DoG wrote: Wed Feb 19, 2020 3:31 pm pm sent to @Icky
Have replied :)
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exxos
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Re: H4 1.44mb modification

Post by exxos »

A small "correction" , I don't think anyone has tested... But you shouldn't need to alter the floppy sel jumpers on the H4 ...
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Tomswork
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Re: H4 1.44mb modification

Post by Tomswork »

How fast do the GAL22V10 need to be

Tom
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exxos
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Re: H4 1.44mb modification

Post by exxos »

Tomswork wrote: Wed Feb 19, 2020 7:16 pm How fast do the GAL22V10 need to be
Doesn't matter.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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People should find solutions to problems, not find problems with solutions.
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rubber_jonnie
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Re: H4 1.44mb modification

Post by rubber_jonnie »

Nice post, I will hopefully work through this today and get mine up and running.
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Re: H4 1.44mb modification

Post by PhilC »

Got mine up and running today, I tried using a GAL20V8B and no luck, it did work with the 20v10 I'd got though.

@exxos will the JED work if its recompiled for a 20v8B?
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Re: H4 1.44mb modification

Post by exxos »

PhilC wrote: Sat May 02, 2020 7:57 pm @exxos will the JED work if its recompiled for a 20v8B?
Wouldn't have thought the GAL's would be compatible ? I don't know what the differences are even ?
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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