UNCLE BERNIE'S IMPROVED APPLE-1 CASSETTE INTERFACE

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Hi ebruchez!

The problem is that the distance between ic sockets A1-A2 (A3-A4) on the main board and the ACI card is different, you can't use the adapter of the respected P-Lab for the ACI card. You need a different board, if I remember correctly Claudio has not yet posted the corrected gerber file for the ACI card. 

 

You might want to take a look at my EPROM card project, there are only a few cheap and distributed components for less than 10$, but you can run some of the most popular programs and games with it.

 

https://www.applefritter.com/content/apple-1-eprom-interface

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ebruchez wrote:I wrote:Mmh,
ebruchez wrote:
I wrote:

Mmh, thinking more about it, I suppose that the content of the ACI PROMs can be included in the EPROMs on the main board's EPROM adapter! In that case, I suppose that the ACI PROM sockets can be left empty. Is my understanding correct?

Thinking further, I realize that I was wrong: the main board EPROM adapter, plug

The ACI PROMs only contain 256 bytes though, don't they?  MMI 6303 are 256x4 each?

 

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About replacing the ACI PROMs ...

... 'softwarejanitor's post #53 is right that the ACI firmware written by Woz is only 256 bytes long, so, theoretically, it could be put into one 256 bytes page of an EPROM adapter sitting in the A1/A2 locations on the motherboard. All you would need is to provide some logic for proper chip select of that EPROM.

 

But here is the catch: the ACI uses another foul Woz trick to save ICs (he is famous for these tricks). The ACI manipulates one address line of the local PROMs on it to make a one bit input port for TAPE IN.

 

How this works is a as follows:

 

- in the address range $C100 to $C1FF, the PROM gets a copy of the original address line.

 

- in the address range $C000 to $C0FF, the PROM gets the TAPE IN signal in lieu of that address signal (see the ACI schematic in the original manual).

 

To test the input port, the firmware running in $C100 to $C1FF reads from a location in $C000 to $C0FF where a change of the TAPE IN signal (from the comparator) leads to two different byte values in the PROM.

 

One problem with this approach is that the CPU will occasionally read an erratic byte when the comparator output toggles close to the end of the PHI2 clock phase. This may cause a read fail as the bogus byte then is used as a compare value  to detect the next comparator output change. It does not happen all too often with bipolar PROMs (they are fast, so the timing window for a read data setup/hold time violation is small) but with a slower EPROM it will happen more often even if you add the input port trick circuit.

 

In my work on the ACI improvements I have greatly mitigated that problem by using the one unused flipflop in the 74LS74 as a synchronizer.

This was part of the Gen1 fixes. Gen1 also removed the need for a negative supply voltage, to make the Gen1 improved ACI compatible with Vince Briel's "Replica 1". The other Gen 1 fix was fixing the totally botched volume indicator LED circuit. Gen 1 also added the 2nd firmware page with my 'extended formatting' routines ($C500-$C5FF) which make the ACI fully Apple II compatible, and also provides autoload and autostart capabilities.

 

Gen2 finally fixed the botched comparator circuit. This involved adding some SMD components hidden under the LM311 socket. This 'Gen 2 improved' ACI PCB which once came with my Apple-1 IC kits currently is only available from Ebay seller newton-computer (as my work was based on his Gerbers).

 

Implementing all these functions on the motherboard is a tall order. Good luck with that !

Tell us how you did it !

 

- Uncle Bernie

 

 

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For someone building an ACI

For someone building an ACI in 2024, there are two issues:

  • ACI PROM sourcing
  • ACI reliability

I'd love to have a solution for both.

A main board option for this would be good to have, but until then, if going with a Gen 2 card, then an EPROM (or other) adapter for the ACI card is needed. I fear that this can be a little clunky, though. A Gen3 or Gen2+ PCB which somehow supports directly an EPROM would be nice :)

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    Hi ebruchez!

    This has all been done before, in 2007 the esteemed Vince Briel developed a cassette interface board with EPROM.

     

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    Macintosh_nik wrote:This has
    Macintosh_nik wrote:

    This has all been done before, in 2007 the esteemed Vince Briel developed a cassette interface board with EPROM.

     

    [[{"fid":"38403","view_mode":"default","fields":{"format":"default","alignment":"","field_file_image_alt_text[und][0][value]":false,"field_file_image_title_text[und][0][value]":false},"link_text":null,"type":"media","field_deltas":{"1":{"format":"default","alignmen

    I wish it were easier to find it / info on making one, I have only seen photos honestly.

     

    I use Bernie's improved gen 2 with my Briel replica 1+. 

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    Macintosh_nik wrote:This has
    Macintosh_nik wrote:

    This has all been done before, in 2007 the esteemed Vince Briel developed a cassette interface board with EPROM.

     

    [[{"fid":"38403","view_mode":"default","fields":{"format":"default","alignment":"","field_file_image_alt_text[und][0][value]":false,"field_file_image_title_text[und][0][value]":false},"link_text":null,"type":"media","field_deltas":{"1":{"format":"default","alignmen

     

    Does anyone know if the Gerners or a project file for that in a CAD app is available?

     

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    Hi softwarejanitor!

    Why do you need it? The project looks a bit bulky, you can make a better simpler one with EPROM 2716, there is enough space and the board will be a bit bigger than the original ACI. And also need a jumper to switch pages if the author's PROM ACI Uncle Bernie's will ever be freely available. It's a couple of evenings' work. If you undertake to make I will give you suitable for editing CAD files of the project Misha Mdesk. But on the condition that it will be an open source project. What do you say?

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