The beginning..

Information about the legacy motherboard project.
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exxos
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The beginning..

Post by exxos »

I have massacred the H5 design :twisted: :twisted:

The same is just simply there at this point until I do a DRAM IC lib.

I have left one expansion socket in there,Thinking in order to keep costs down, things like flashy clock should be a optional extra. But socket I hope to actually rotate it and put it vertically so the entire bus runs from left to right of the motherboard "via" the 68K socket. to do this I will likely move the shifter to the left and maybe even flip that vertically as well.

I'm going to try and leave the blitter in there, it is still a legacy chip and I think it would be a shame to remove it.. It really depends on space..My aim is to literally cut the board in half just in front of the power supply

The GLUE will be relocated to the right side of the board near the MFP, likely the CPU will end up there as well. This will allow me to have the DRAM and MMU under the power supply and right next to the shifter doing away with those diagonal green traces which run the fairway across the board was actually caused a huge amount of routing problems.

A lot of the mods will be left in place such as the integrated video switch (like UBE adapter) , 1.44 floppy GAL, all the usual DMA fixes etc. While it is a legacy machine, I still want to add on things which people most likely use anyway such as the UBE adapter. It helps to give the board a little bit more value and user-friendliness as well.

I also want to point out that I'll be working on this board behind the scenes and I am really not looking at it being finished for at least 12 months. I really want to take my time with the design of this and get it to a point where I'm happy with it, So might as well make it 24 months :lol: Again because of my RSI work on this will be slow, but I may have to redo parts of it several times to get the best layout anyway. Once done, I will "resize" the motherboard down as much as possible.

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Re: The beginning..

Post by exxos »

Started the first draft layout. CPU, BLITTER,GLUE under the floppy drive.

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Re: The beginning..

Post by exxos »

Looks like I can squash a lot of chips under the floppy drive...

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Re: The beginning..

Post by exxos »

Among other things I've been working on this on and off all day again..Mostly just sitting staring at it :shock:

In the end I decided to remove the PLCC MFP and put back the DIP. Mostly because it will save me having to solder the PLCC, and while 2 sides of the MFP Rooted really nicely, the opposite sides everything was just backwards :roll: Having space in between the pins makes routing a whole lot easier and neater.

I also had a similar problem with the MAX238 chip. No matter how it was routed, everything was just in the way of everything so I went back to the DIP package, albeit it is more expensive :(

I also did a lot of experimenting with having the three PLCC chips (68K,BLITTER,GLUE) all facing upwards, but the routing just turned into a total nightmare unfortunately so they all have to be rotated. It would have been nice to have the more facing upwards. The autorouter can do it , but I want to route this all manually to get the best layout possible.

I've also started working on draft layouts for the DMA area also. Have to be it for a while now was all the clicking is taking its toll again :(

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Re: The beginning..

Post by exxos »

Bit of tidying up and a few more tracks done.

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Re: The beginning..

Post by exxos »

The SMT chip in the middle of the above image, is the NAND gate for the MFP and YM chip. I'm not very happy on its routing or location.. I did try using a smaller 2 gate chip so I could split them up, but did not really seem to help at the time.

Now some more routing has been done, I thought I would reroute the MFP logic to the GAL instead. I had to move a lot of pins around anyway to make the routing easier so added in the equation...

Code: Select all

IO5 = !(1772_INTRQ & !HDINT);
Basically a NAND where HDINT is inverted. So unless I've done something stupid, it should be the equivalent circuit.

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EDIT:

OK that NAND symbol is wrong, its actually a NOR :roll:

Code: Select all

IO5 = !(1772_INTRQ # !HDINT);
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Re: The beginning..

Post by exxos »

Slowly but surely...

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Re: The beginning..

Post by exxos »

Still plugging away in the background on and off with this project..

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Re: The beginning..

Post by exxos »

So near and yet so far....

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Re: The beginning..

Post by exxos »

yay!

Need to do a epic of tidying up yet though...

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