Minimig PCB run - interest thread

[skurk]

Xenepp wrote:
As it goes, this thread's gotten pretty long, should I start a new thread for pre-orders so no-one misses out?

Start a new thread, take PM's, leave your email or home phone number - I don't care as long as I'm on that list

I'm still in for two pre-assembled boards.  I have a few friends who are interested too, so it might even be five.  I'll let you know the final number once we figure out how to pre-order properly.

[Belial6]

PM Sent.

Preferably a pre-assembled, but if they are all taken, I will take a bare board.

[Xenepp]

All pre-order discussion should now be directed here:

http://www.amiga.org/forums/showthread.php?t=30997

Full details are outlined there and those who have PM'd me (already!) should check there to make sure they are still in and let me know.

 -Joel

[freqmax]

What will the v1.1 board improvements be ..?
* Or gate between fpga/mmc spi?
* Spi_dout fpga patch?
* Pin headers?
* DCM generated color clock?
* One or two SRAM chips?
* Video D/A resistor ladder linearity fixed?

Btw, is it possible to make the mc68000 behave like a mc68020 or such via fpga tweaks? (and make aga or such feasable)

[Xenepp]

Improvments are mostly fixes and part reduction from what Dennis tells me.

Swapping the 68k for an 020 is possable with changes to the schematic and the FPGA core. Both require lots of time and patience, but I would expect someone will have a go at making upgrades at some point.

 -Joel

[TheMagicM]

I will take a pre-assembled V1.1!!!  I'll PM you NOW!!

[freqmax]

Xenepp:
I think you misunderstood me. My idea is weather it's possible to "fake" a mc68020 with a mc68000 using the fpga that sits like a spider in the wire network. Ie using only hdl (verilog) tweaks.

[Xenepp]

Sorry freqmax, I'm not following you  :-?

To "fake" the 020 is folly. As soon as any software that needed it was run it'd crash, as to the software, the hardware would be "failing".

The only way 020 programs would run would be to impliment the hardware and reconfigure the design to match.

Unless you mean to just impliment the 020 exclusive features the the FPGA then have the 68k handle the rest, that could be possable I guess, but if it was I'd expect it to run real slow :-)

 -Joel

[freqmax]

Xenepp:
Well the idea was to just implement the 020 exclusive features  in the FPGA. And let the present 68k handle the rest.
(makes me wonder how hard it's just to swap the current 68k to something else, pin compatible?)

Dennis:
Are crystals X1 and X2 operating in parallel or serial resonance mode?

For pcb v1.1 makers:
I have sorted the issues I have discovered and found mentioned on amiga.org here:
http://www.opencircuits.com/Minimig_Board_v1.0_documentation

There's a non obvious issue with the video D/A. The original resistor values cause a dent in the desired vs actual output value. The math and results are here:
http://www.opencircuits.com/Minimig_Video_d/a_resistor_ladder
My patch also make better use of the full signal swing available.
In short the resistor ladder should use 4220 ohm, 2100 ohm, 1050 ohm, 523 ohm (1% tolerance). In order to avoid this.

I also found that the output D/A also needs a translation table to match input data with correct output amplitude due how ohms law works. Anyone found this in the verilog sources? Amber & Agnus is likely candidates..

[alexh]

freqmax wrote:
makes me wonder how hard it's just to swap the current 68k to something else, pin compatible?

Only thing you could have possibly swapped it for would have been a 68010 but they dont make them anymore, and I doubt they ever made SE variants. 020+ wouldnt be pin compatible. With a few wires and a lot of patience I am sure you could wire on any CPU mounted A500/A600 accelerator.

freqmax wrote:
In short the resistor ladder should use 4220 ohm, 2100 ohm, 1050 ohm, 523 ohm (1% tolerance).

Q. Can you get SMT resistors of such wild values?

[Xenepp]

The thing is, you would need to alter the FPGA program even if the 020 was pin compatable since the architecture is still slightly diffrent and the rest of the hardware on board would need to know this, or be upgraded to cope with it.

A good example is the Sega Megadrive. I remember a few years ago, a few people were tinkering with it trying to squeeze more speed out of the 68k. They upgraded it with a faster chip and all kinds of wacky things happened in some games, most wouldn't even boot. That was still using a 68k.

 -Joel

[zetsurin]

Apologies for this slightly OT post... Anyone in London able to help me assemble one of these things?  I can solder but just barely.  Wish I put more time into trying to improve things in that department!  Would be good to have a big group Minimig buildathon

[tonyyeb]

In the other thread it says preassembled will be limited to two per person. I think this should be 1. Then at least more forum members will get a chance at owning one. If i could solder well enough i would build it myself but as i cant i would like an assembled one.

[freqmax]

alexh wrote:
Q. Can you get SMT resistors of such wild values?

Value  - Digikey ID
523    - RR12P523DCT-ND
1.05K  - RG20P1.05KBCT-ND
2.1K   - RR12P2.1KDCT-ND
4.22K  - RR12P4.22KBCT-ND

Package 0805, 1/10W, Thin film, 10 pcs/order asfair.
Total cost ~2 USD.

Actually when I did the math the thing I was looking for were the available resistor values. The most important is to check that Vpp-peak is lower than 0.7V at all times. So the values may be wild for humans. :-D But they fit digikey ordering and the equations.

As for improvements, how about wire the mcu spare i/o to another pin header?  (just like it's done on the fpga)
http://www.opencircuits.com/Minimig_MCU_user_I/O

[dammy]

AROS could use some devs to bring AROS 68K out of unmaintained.

Dammy

[nBit7]

Q. Can you get SMT resistors of such wild values?

The values listed are the "preferred value" for 1% resistors as defined by an EIA standard.

http://www.pc-control.co.uk/resistor-eia.htm