AddZorro2slot

NOTE: this is an "Html translation" of the project I put on Aminet as hard/hack/AddZorro2slot.lha
A partial porting for the A1200 can be found here

Copyright and Distribution

This project is freeware, even because I invented nothing; I only read the manuals and the A500 and A2000 schematics. You can send me whatever you want, just to tell me if you liked it or not. It can be distributed everywhere but please keep the archive intact.

History

I own my Amiga 500 since 1988.
As the AGA Amigas were available I was not so excited. The specs was not so great compared to my system ( and compared to the "soon upcoming" AAA chipset), so I decided to wait. You all know what happened a couple of years later ....
Now I'm here waiting for a PPC Amiga, but in the meanwhile I added to my trusty 500 the only thing it missed: 24 bit graphic ! There are a lot of graphics boards for A2000, but none for A500, so I compared the schematics of the two systems and I added a full (?) 100 pin Zorro2 slot to the 86 pin expansion port of the A500
(NOTE: This hack allows to ADD a 100 pin Zorro2 slot keeping intact the 86 pin expansion port !!!!).

Limits

My system works great since March 1996.
If I'm not wrong the A1000 has the same 86 pin expansion port as the A500, so this hack, probably, can be adapted to work with this machine too.
I give NO WARRANTY this hack will work with different configurations; you had to try by yourself and at YOUR OWN RISK !!! If you do something wrong the consequences are unpredictable: maybe your Amiga won't work and removing the hack will solve the problem, but it's possible that you BLOW UP your computer and I have no responsibility !!!!
I chose a Picasso II, so this project is realized around it. This hack uses NO EXTRAS CHIPS (in particular there's no Buster), thus this slot can work with other than graphics boards but I think only one board can be DMA (I have some doubts it will work with GVP boards, because they use DMA). Also a Firecracker24 worked good with this hack.

Theoric realization

With reference to the included pic, the straight lines are really used by my Picasso II board; dotted lines instead are possible links but I didn't tested it. The description is referred to my configuration; you have to change my SCSI controller with your device inserted in the 86 pin expansion port, and my Picasso II with the board you want to insert into the new slot.

Here I list the 100 pin Zorro 2 slot signals on the left, and the corriponding signal taken from the A500 on the right. If in your user manual there are the schemes, it can be useful to give it a look sometimes. Better if you can compare the A2000 and A500 schemes. There are some references to another hack I found on Aminet called 2000slot.lha which can be found in the hard/hack directory (but this hack only allow to transform the 86 pin expansion slot to a 100 pin Zorro 2 slot); anyway it can be useful to give it a look.

Almost all the links are taken (shunt connection) directly from the 86 pin port, so you can solder a wire between the two corrisponding pins (one on the Amiga, the other on the new slot).

The CONFIG_IN* and CONFIG_OUT* signals are connected "serially": the CONFIG_IN* from the 86 pin expansion port is connected to the Picasso's CONFIG_IN* pin; the CONFIG_OUT* signal from the Picasso is connected to the CONFIG_IN* of the board inserted in the 86 pin expansion port (e.g. my SCSI controller); Probably it's possible to change the config order (first the SCSI controller, then the Picasso) but my SCSI board has no CONFIG_OUT* signal.
NOTE: it's important that the CONFIG_IN* of the 86 pin expansion port goes to only one board or you'll have auto-configuration conflicts !!

The BUSRST* signal is taken from a 74LS32 chip on the A500 motherboard (under the internal floppy drive); the 68000 RST* signal makes there a NAND (with negated inputs) with 0, thus it exits unchanged but more stable (and a little delayed), and then goes to the #94 pin of the Zorro 2 slot. I tried, before, to use directly the RST* signal as BUSRST* but I had some conflicts between the Picasso and the accelerating board during the reset sequence (I think both boards tried to autoconfig itself in the same time and/or in the same addresses).

Practical realization

I rate the realization quite simple if you are expert with soldering and testing electric circuits, quite hard (and dangerous for your Amiga) if you have no idea about what you're doing.
You had to be very patient and make everything slowly with calm.

NOTE: my project uses NO EXTRA CHIPS !!!

It was impossible to me to found a 100 pin slot.
I went to a computer reparation center and there I obtained, for free, a non-working 286 motherboard. I rip off from it 2 ISA (?) slots (62 pins each); I cut it in the way that they can be aligned to form one 100 pin slot (once the Picasso is inserted they won't move).
Then I used a 50 wires flat-cable (two 9 cm long pieces, aligned; keep these cables as short as possible !) to make the connections between the 100 pin slot and the 86 pin expansion port.
Note that the numer one pin on the A500 is to the rear of the upper side of the motherboard, but the number one pin of the 100 pin slot is (looking at it from above) to the rear of the left side.

I made all the solders in the "vias" (holes which bring a track from a face to the other) on the SCSI board; the SCSI board is inserted, with its slot, in the expansion port and the flat cables bring the signals to the new Zorro slot. Probably a look to some snapshots can explain it better.

If you can't do like me, probably you must think about some other way to connect the boards; you can make a connector which duplicates the signal of the expansion port (from each pin start two wires, one for the 100 pin slot and the other for the SCSI controller).
Other wires can be used for the BUSRST*, 7MHz, -5V,... connections.
You have to make all the connections your new Zorro 2 board requires.
CHECK EVERYTIME IF THE CONNECTION ARE NOT FAULTY AND THERE ARE NO SHORT CIRCUITS !!!

Credits, thanks and greetings go to:

My brother Leonardo, for his insistence which push me to conceive and realize this project.

Dr. Segio Congiu, my Electronic Computers professor, who made me understand what I was doing.

My friends Massimiliano Farnea, Zeno Montresor, Michele Bianchi and Eugenio Perinelli for their technical,theorical and moral support.

Piergiorgio Sartor and Paolo Canali, ever ready and gentle to answer my technical questions.

Greetings to:

The Amiga community of the Padova University, the worldwide Amiga community, the Amiga Report staff, the Amiga Internaional team, and everyone who knows me.

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