Minimig PCB run - interest thread

[freqmax]

FrenchShark wrote:
It could be possible with a 27 MHz XTAL.
See the page:
http://www.opencircuits.com/Minimig_NTSC
Here is the computation:

27,000,000 / 429 x 455 = 28,636,363 (NTSC clock, 0 ppm)
27,000,000 / 432 x 454 = 28,375,000 (PAL clock, 6 ppm)

The DCM from the Spartan 3 accepts only coefficients from 1 to 32 :-(.
The Cyclone III accepts coefficients from 1 to 512.

The NTSC clock generation can be simplified to:
27,000,000 / 33 * 35 -> would fit into 2 cascaded DCMs.
We are less lucky with the PAL clock generation:
27,000,000 / 216 * 227 -> 227 is a prime number !

Could you explain your equations a little bit more?
27/4.433619 = 6.0898331 ie divide by 6 ..?

[mongo]

Talking about that (and I don't mean to sound ungrateful) I would have thought Composite/S-Video would have been a necessity on this thing, considering how console-esque it is.

An Analog Devices AD723 could be used to generate both Composite and S-Video output from the MiniMig's RGB.

Probably add about $6-7 to the cost of things.

[narmi]

Adding composite/s-video output would take up precious board space.  You need several components in addition to the encoder chip, including some large electrolytic capacitors, and possibly one or two clock sources.

[mongo]

narmi wrote:
Adding composite/s-video output would take up precious board space.  You need several components in addition to the encoder chip, including some large electrolytic capacitors, and possibly one or two clock sources.

The AD723 does not require output capacitors and the clock can be supplied by the FPGA.

[dammy]

Anyone know what the max size ROM a minimig can use?

Dammy

[freqmax]

It currently allocates 512k out of 2M as kickstart memory. With writes disabled. Any change to this can be done by changing fpga configuration.

[FrenchShark]

freqmax wrote:
Could you explain your equations a little bit more?
27/4.433619 = 6.0898331 ie divide by 6 ..?

28,636,363 Hz and 28,375,160 Hz are the base frequencies of an NTSC and PAL Amiga respectively.
As discussed before, they can be generated with a single 27 MHz crystal.

Why did Commodore used these frequencies ? Because :
- the PAL color clock is 5/32 of 28.375160 MHz (i.e. 4.433619 MHz)
- the NTSC color clock is 1/8 of 28.636363 MHz (i.e. 3.579545 MHz)
-> That way, you have got a video compatible computer.

Dennis used a 4.433619 MHz crystal  to generate the 28.375160 MHz and all the sub-multiples.
I guess he did that because the 28.375160 MHz crystal was not available.

[Dr_Righteous]

Oh, add me to the list of the interested. Form factor doesn't matter. Original would suffice. I'm hoping by the time they're ready I'll be out of my financial woes.

[JosephC]

I want minimig with PAR: so I can play 4 player adapter games.
And I need a hard drive so I can use Deluxe Paint 5.

And I need it to work like my REAL Amiga 500 which REALLY lets me switch back and forth from a NTSC to PAL display in REAL time anytime I want. A REAL Amber chip happily deinterlaces a 50hz or 60hz signal so I don't get what the problem is. A REAL Fat Agnus chip instantly switches to PAL or NTSC by setting the correct bit. If minimig was REALLY hardware compatible then it would work already.

[amigadave]

@JosephC,

Minimig's creator never claimed that it was "hardware compatible" with all A500 chips, just that he was trying to make it able to run "most" OCS Amiga games.  I don't think he ever intended it to be a complete replacement for Classic Amiga computers.  It was just a fun challenging project to see if it could be done.  See Jens "A-Clone" project, which is more like what you are asking for, a complete hardware replacement of the custom chips on an A500.  Jens demonstrated it at AmiWest last year where he had completed the replacement of 2 or 3 custom chips with 100% accurate function by plugging his PCBs into the chip sockets.  Once he has completed the designs, I believe his plan is to put the replacement designs into silicon and we will finally have a source for replacement custom chips for the Amiga and possibly a way forward to some enhancements to the original Amiga designs.

I am writing all of this just from my questionable memory without going to Jens website to confirm, so take it with a grain of salt and go check out what Jens is doing for yourself.  Minimig is a completely different project with a different purpose.

My 2 cents,

[zetsurin]

Very interested in an assembled board.

[gameaholix]

i'd be interested in two or three populated or unpopulated, and add my vote for modular ports.

[freqmax]

I think the unfortune fact is that there are no free pins for a parallel port on the fpga.

[techie]

@amigadave

 See Jens "A-Clone" project, which is more like what you are asking for, a complete hardware replacement of the custom chips on an A500.  Jens demonstrated it at AmiWest last year where he had completed the replacement of 2 or 3 custom chips with 100% accurate function by plugging his PCBs into the chip sockets.  Once he has completed the designs, I believe his plan is to put the replacement designs into silicon and we will finally have a source for replacement custom chips for the Amiga and possibly a way forward to some enhancements to the original Amiga designs.

I am writing all of this just from my questionable memory without going to Jens website to confirm, so take it with a grain of salt and go check out what Jens is doing for yourself.  Minimig is a completely different project with a different purpose.

My 2 cents,

Correct me if I'm wrong but I don't think it was Jens intention to create replacement custom chips for the Amiga from the Clone-A project :/
(though admittedly my memory may be a bit off about this)

From what I remember reading in the article from Total Amiga a few months back, it sounds to me like the aim of that project was more along the lines of a Amiga in a joystick and/or a mini-itx board with scan doubling/flicker fixing built in.

Either way it goes I personally plan to support both the Minimig project and Clone-A. Though I am really[/] excited at the prospect of what Jens might create in a Clone-A mini-itx format :-D

[Fixer]

techie wrote:
Correct me if I'm wrong but I don't think it was Jens intention to create replacement custom chips for the Amiga from the Clone-A project :/
(though admittedly my memory may be a bit off about this)

From what I remember reading in the article from Total Amiga a few months back, it sounds to me like the aim of that project was more along the lines of a Amiga in a joystick and/or a mini-itx board with scan doubling/flicker fixing built in.

You're correct it was never the ultimate goal to replace the custom chips, but it WAS one of the stages.

I remember at one point cycle-accurate custom chip replacements were being showcased in an original A500.

This is how the move forward to recreating and improving the original Amiga chipset is being done!

Both the Minimig and Clone-A projects are interesting and serve different purposes. However the fact of the matter is we have only one completed so-far and that is Dennis' Minimig.

I'm sure Jens will come through though - one of the few good guys left.

[McVenco]

I'll buy a completely fabricated one, no matter the form factor...