Amiga hardware info, help and support with a focus (but not limited to) North American NTSC experiences. Open to all.
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JEY08
Bath, MI

by JEY08 posted Fri Dec 14, 2018 7:11 pm

intric8 wrote:OK very cool. I'll get this front expansion sent your way stat.

Mattsoft had a cool idea while pondering your system:
It would be cool to take your daughterboard and put it on a known fully working system and see what happens just to get a benchmark.

That's a good idea. If the replacement memory board doesn't solve the problem then we'll have to try that.
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JEY08
Bath, MI

by JEY08 posted Fri Dec 14, 2018 7:15 pm

I've made progress on the schematic of the daughterboard modification. I'll post it soon. I'm try to understand it right now. :shock:
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JEY08
Bath, MI

by JEY08 posted Sat Dec 15, 2018 9:57 pm

I think I've got it figured out. Here is the schematic of the daughter board modifications.

https://drive.google.com/open?id=1UAkYJs8v8v8YPKY6vrlqyklNvO0zYuVa

The motherboard piggyback is the normal one except the lead that went to the daughterboard now goes to pin 1 of U5L on motherboard which is address line A23.

The modification makes the piggyback RAM appear starting at location C00000. With the address number going as A0...A23 that address would have ones in A22 and A23 with the rest zeros.

The circuit shown basically passes the original A23, A22 states to A23M and A22M if the address is outside of the region chosen for the piggyback ram. It's like the modification isn't there. To be within that region A23=1, A22=1, A21=0, A20=0, A19=0. It will be outside if any of those values changes.

When the 68000 does a read cycle is turns on the AS* address strobe output to the DPALEN pal U5L. When the address is in the right range it turns on the RAM enable RE*. If you look at the logic equations for DPALEN the right range is when A21-A23 are all 0.

The logic equations for the PALS are here: https://drive.google.com/open?id=1FcBPov4R692_s4LvYy-GmcY8QLi4CsXK

However A23 and A22 are 1 when we're at C00000. What the logic circuit in the mod does is supply 0 to the new A23M and A22M lines to DPALEN. Then DPALEN is able assert RE*.

A23 is 1 though so the line to the piggyback RAM is now enabled. The existing motherboard decoding does the rest.

The schematics and basic operating theory of the A1000 can be found here: http://www.devili.iki.fi/mirrors/4x4.hopto.org/

It was a very clever way to avoid having a lot of address decoding and also puts the ram in a location that won't be misinterpreted as chip ram. I'm amazed that anyone came up with the idea. I wish I knew who they were.
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JEY08
Bath, MI

by JEY08 posted Tue Dec 18, 2018 6:01 pm

Eric's front memory unit works in the A1000 so the problem must have been with mine.

A1K_Mem2.jpg
A1K with new front mem.


It's all there.

I picked up a 3.5" Toshiba floppy drive that looks just like the A1000 floppy drive. It has jumpers for rdy, dc, ds=0-4. I assume I'll have to switch disk ready and disk change, but I'll try it as is first.

A1000Drive.jpg
New drive
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intric8
Seattle, WA, USA

by intric8 posted Wed Dec 19, 2018 9:53 am

So glad to hear the front memory worked!
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intric8
Seattle, WA, USA

by intric8 posted Wed Dec 19, 2018 9:56 am

What's the model number for that Toshiba? Is it a straight drop-in replacement? That would be epic.

I had to change a drive out on my Phoenix and it required drilling new holes in the original steel bracket. Total PITA. Plus the eject button had to be created from scratch. Luckily Mattsoft has mad 3D modeling and printing skills and was able to help out massively.
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JEY08
Bath, MI

by JEY08 posted Wed Dec 19, 2018 6:32 pm

The model is FDD 4561A0K and it's ebay item number 362435548414. It looks like he just raised the price.

I haven't tried it yet. It looks like it might not be difficult to swap 2 and 34 if necessary.
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intric8
Seattle, WA, USA

by intric8 posted Wed Dec 19, 2018 8:15 pm

That is some cool NOS/NIB gear there.

This is the drive I used. It's a lot quieter than the stock drive, but like I said before getting it in there was tough. Plus, the 3D printed button that came with it was intended for the A500 and was too shallow for the 1000's case. Thankfully Mattsoft was able to rectify that issue.

Looking forward to seeing how yours goes!
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intric8
Seattle, WA, USA

by intric8 posted Wed Dec 19, 2018 8:16 pm

Hrm... I spy an A4000. And original Marble Madness disk! ;)
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JEY08
Bath, MI

by JEY08 posted Thu Dec 20, 2018 7:43 am

intric8 wrote:That is some cool NOS/NIB gear there.

This is the drive I used. It's a lot quieter than the stock drive, but like I said before getting it in there was tough. Plus, the 3D printed button that came with it was intended for the A500 and was too shallow for the 1000's case. Thankfully Mattsoft was able to rectify that issue.

Looking forward to seeing how yours goes!

I would miss the noise!

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