Amiga 600 schematics nearly put into Kicad

[JimmyH]

If I had done this I had removed the whole CXA part and antenna/rca output. The later could be used for vga/hdmi and ps2 connections. You would also loose alot of potentially leaking caps in the future. The space left after the CXA circuit could be used for new things like dedicated cf slot on board and have the ide port as slave/master port with a jumper.

[Mick]

Hi Jimmy. I'll be releasing files just as soon as I can check hole dimensions/diameters with a real board. I think we all want different things that's why I'd rather make a base version and people can branch off in their own directions. There may still be errors in the schematics I've done but the way I see it I'll saved anyone who uses the files about 3-4weeks of work by doing the monotonous stuff.

I know very little about creating electronic circuits, I just learned to use Kicad and the rest is just following the plans (schematics). I think anyone on this forum could do it if they learn to use Kicad and dedicate the time. Like I said in the original post it was Kai's memory converter board that inspired me to have a go with KiCad trying to make one myself.

I quite like the 2MB onboard memory and direct all CPU signals to the expansion connector idea myself but I'm not sure if I could do it, looking at the Amiga 500 schematics for the Zorro connector there's a few capacitors coming off some of the signals and I have no idea why. Why do capacitors/resistors even exist?

[go0se]

Originally Posted by Mick

What are the female connectors the A600 uses for expansion cards and are they available in bigger sizes? I'm wondering if I could extend the existing connector with a lip so that it doesn't block existing cards?

Hi Mick,

The expansion connectors you asked about can be found on Mouser with a datasheet.

https://www.mouser.co.uk/ProductDeta...vM3aFp3w%3D%3D

Or, to get them at a better price in the UK :

https://coolcomponents.co.uk/collect...-bbc-micro-bit

I'm not sure if they are available in different sizes but standard PCI connectors are also the same pitch I think.

[Mick]

Ok thanks go0se that's handy information. I was just looking into theoretically extending the current connector but it wouldn't work because so few of the CPU signals go to the current connector and there's not really enough room to add another 60 or so, amongst other things. I think my idea of having 2MB RAM and clockport on the mainboard and creating an A600 mini-Zorro out of the current connector would be the neatest way. Hopefully someone will try it. nudge nudge wink wink. I'm sure people can make PLCC to dip converters that sit on Denise in order to keep Indivision support.

Oh and welcome to the forum.

[Stedy]

Originally Posted by Mick

I've spent most of the day routing power since there are varying track widths, could anyone explain the AGND (analogue ground?) to me please? is it connected to a separate ground plane to the rest of the motherboard? should I isolate it from the rest of the ground plane? or is it all just connected to the normal ground but close to the RCA's?

Also what board manufacturers do people recommend, I had a look at the one Kipper posted but they only do 30x30cm on more than 2 layers?

Hi,

AGND is indeed analogue ground. It is used for the audio circuits and some of the video functions on the A600 (don't have the schematics open to double check). The old school way of doing it was to have separate digital GND (DGND) and analogue ground (AGND) and tie them at one point. The placement of the tie point was 'challenging' and could easily cause current loops, which you don't want. The modern way is to have named AGND/DNGD signals but route them on one or 2 layers but partition the sensitive analogue parts by bisecting the power planes. Placement of parts becomes more critical to achieve this.

https://electronics.stackexchange.co...und-connection

For PCBs, look at https://pcbshopper.com/.

[Mick]

Thanks Stedy I think I understand it now, it looks like it's connected to the same ground at the RCA connectors but the ground in that area is heavily isolated from everything else. I wasn't sure if it took its ground connection from the speakers or something.

I have the whole of the 2nd layer as a ground plane, would it be better to isolate the ground of the audio RCA's from the ground layer and connect them directly to the power connector ground via traces?

[Mick]

Does this look like a good ground layer? I've separated the analogue portion a bit?



Apologies for all of the annoying questions but this is a learning process for me.

edit: I've just realised I don't need to extend the plane so far into the edge connector, or will the extra copper add strength?

[Stedy]

Originally Posted by Mick

Does this look like a good ground layer? I've separated the analogue portion a bit?



Apologies for all of the annoying questions but this is a learning process for me.

edit: I've just realised I don't need to extend the plane so far into the edge connector, or will the extra copper add strength?

That looks fine for a AGND/DGND split
I've found a few errors in the schematics, have not finished the checks yet, will post the list once complete and amended schematics.

I have a few simple ideas to remove some obsolete parts and make some room, but get the basics right first.

Are you using 1206 size resistors/capacitors as per the original design?
We could shrink to 0603 on a lot of them and gain some PCB space.

Will continue checks tomorrow.

[Mick]

Thanks Stedy. I've fixed a couple or errors since last time myself as I had a careful look through, I think one was power global labels put the wrong way around on one of the IC's and a couple of junctions either missing or added where it shouldn't.

Stedy do you have A600 motherboard? I've been trying to borrow one but not heard back after messaging a few days ago. I'd ideally like to check mounting hole dimensions and diameters before releasing layout. If you have an A600 board and can help check dimensions PM me your email address and I'll send files.

I followed the A600 service manual for footprint sizes but I generally chose "Handsolder", it was just the MELF that I went with normal since handsolder were huge.

If I had the circuit knowledge I would release files for this and then work on an "enhanced" version with the extra 1MB/clockport and Zorro connector I mentioned earlier, perhaps use a longer connector so people can't plug standard A600 cards into it and also include some of the old signals if needed. I think the memory is a straight link up plus a couple of decoupling caps but not sure about the Zorro and the clockport has some _PWR_BAD signal that doesn't seem to connect to anything in the A1200 schematics.

edit: I changed the symbol for D571 as I noticed the pins were mixed up.

[kipper2k]

Hi Mick,

I have been giving this project some more thought and i think it is a great idea. The one thing i want to see is the capability of the board to allow addons and plugins for accelerators etc. When people make their boards they normally use sockets as it is a safety net so to speak in case you get a bad chip. The thing is, the CPU cannot fit inside a socket as the A600 needs a PLCC socket to be placed on top of it upside down to (try) to get a good connection when trying to use addon boards.

If a person solders the CPU directly onto the motherboard then they really need to do a very good job or they won't be able to get a socket over the top. this will limit the amount of people willing to take on the build challenge. This is the reason why i was hoping that the CPU signals can be broke out into a header/s so that people can tap into them.

Board houses now offer 0.0035" traces and 0.008" vias on a 4 layer board which make the layout much more easy to adapt.

(my tuppence worth

edit; another suggestion; using a 2mm header (same as used on the HDD) could be used, it does not take up a lot of space and would give a positive connection, you could use 2 x 34 headers in the 4 row configuration

[Mick]

Hi kipper,

Would you be happy with the expansion slot being turned into a Zorro or do you want a header specifically? if I add the CPU signals to either a header or slot at some point do they need any capacitors/resistors hanging off of them like the A500 schematics show? I don't really understand the electrical side of things but hopefully Stedy will be helping me going forward. Also, if I were to turn the slot into a Zorro are any of the signals in the standard slot still useful if the board has 2MB ram onboard and clockport?

I am just going to try to get a basic/reference board out first that follows the schematics as closely as possible and then once it's confirmed working we can start getting creative. Stedy is wanting to replace the 23pin D-Subs etc and there's been various requests for things here. I just want to get a reference board out first as a starting point. I'm not bothered if everybody waits for modified ones, I'm not looking to make money. My plan is just to release the files and people can modify or use them to get their own PCB's made, hence why I don't want to release files with misaligned holes etc.

This whole thing just started as me messing around in Kicad and then having the crazy idea to try to draw up the A600 schematics and see how far I could go. I'm not as clued up with the electrical side of things as the other designers in the community.

[kipper2k]

Hi Mick, i don't want to discourage you from this project, if you want to make it authentic then that is perfectly fine. If you are going to release the files on completion then someone else can do their own updates.

The A600 really wasn't well thought out as regards upgrade-ability, i think it was cut, copy and paste and get it to market quick. There are a few accelerator boards out there for the A600 now and i think people would like to either take advantage of current boards or boards that could be created if the a600 was more friendly

[Mick]

I could have a go at turning the expansion slot into a Zorro in another revision but I'll probably need help with the circuit if it requires more than just directing the raw CPU signals to the contacts, also I am not not sure what signals in the standard A600 connector (if any) should be kept. It looks like a couple of them carry audio which might be useful? Do you like that idea though? I think it's the neatest way to add accelerator support without having to clip onto the CPU.

[Mick]

It's just about complete from my point of view, I'm just waiting on Stedy as he is comparing the layout to a real board and then I was going to unleash the files so anyone can modify it the way they want without having to go through the weeks of work I have.




I manually routed power, ground has a dedicated plane, 6mil/6mil track width/distance for signals. Freerouting spent about 2 days getting it down to around 1300 VIA's, 44Million track length. So there's my adventure in KiCad.

[Heywood]

Nice work Mick!

[Mick]

Hi Heywood, thanks. I know there were a few requests including yours but the hope is people can DIY a board to their own unique preference or someone will make a modified version with all of the extras people want. I'll plant the seed others can grow and nurture the crop.

If anyone is interested in learning KiCad look for Kai's memory converter PCB and try to replicate it yourself, it's a good way to familiarise yourself that's how it all started for me.

[kipper2k]

looks great Mick, when are you going to build it I notice below the rom there is a lot of empty space, i think that could be utilized for headers as long as it is low profile as the KB sits close. A lot of cpu signals can be taken from the rom and custom chips so routing does not necessarily need to come directly from the CPU itself (I have never used Kicad

[Heywood]

Originally Posted by Mick

Hi Heywood, thanks. I know there were a few requests including yours but the hope is people can DIY a board to their own unique preference or someone will make a modified version with all of the extras people want. I'll plant the seed others can grow and nurture the crop.

If anyone is interested in learning KiCad look for Kai's memory converter PCB and try to replicate it yourself, it's a good way to familiarise yourself that's how it all started for me.

Hi Mick, I've been playing with KiCad a bit with significantly less complex PCBs so I have a rough appreciation for your work - working within the existing footprint and needing to leave connectors where they are is probably a hassle compared to making a workalike.

The number of vias in your board sound like a lot on the surface - just needing to control-shift-v and then pressing E to associate the VIA with a net that many times must have been draining. however when you consider the ratio of surface mount components to through hole, it is completely understandable you needed it (and I'm sure you were working to reduce how many you put there)

Regarding requests from others regarding customisations - I completely understand you had your itch to scratch and we are particularly fortunate that you plan to share your work with the rest of us so if we chose to make additional changes, the amount of effort required will not be as significant as yours.

Once again - nice work!

[Stedy]

Hi,

Still checking schematics, so the delay in releasing files is due to me checking everything! Once schematics are complete, it's on to the PCB. Easily 20-30 hours to check a design like this.

When measuring my A600 yesterday, I noticed the original was only 2 layers! It has tightly coupled traces going vertical on the top layer and horizontal on the bottom layer. This approach would only work with old school, slow speed TTL, with modern fast logic, the crosstalk would kill the PCB, unless you sent to controlled impedance. What I'm saying is that it's a clever design for the technology of the time.

@kipper2K & mick
You do realise there's very little skyline where the RAM expansion fits, <10mm at the end?

There are many ways you could soup up the design, from easy to hard:
1) Mix L/R audio by 30%, using 4 resistors to make the audio less harsh.
2) Add some simple TTL logic to switch SEL0/SEL1 + MTR to allow DF0:/DF1: to be swapped for Gotek drives. Based on A4000 schematics.
3) Remove the RCA composite video connector and fit a 4 pin mini-din for S-video from the CXA1145/CXA2075 encoder. Connect Y to C via 100pF if you need composhite.
4) Remove the 23 way video connector, fit a HD15 VGA socket and a 4 pin mini-DIN (if you don't do option 3) in the space. Could also add the SCART/VESA VSIS fixes to the Amiga Sync signals to allow easier connection to video scalers/TVs.
5) Remove the RF modulator and the 5 pin square DIN plug. Fit a 2.5mm DC power plug and add a 12V to 5V converter and a -12V inverter. This provides a high current power supply for the unit by freeing up some space.
6) Fix the Amigas incompatibility with Type 1 compact flash cards on IDE by adding 74HC series TTL devices to correctly shift the IDE/CF signals to 5V CMOS levels.
7) Add the extra 1MB of chip RAM to the design by growing the PCB into the expansion slot. Maybe add a 8MB add-on?
8) Add a CPU connector slot.

It's easy to type this, to design, build and test takes time.

[hooverphonique]

Hi Stedy,


what do you mean by

Originally Posted by Stedy

tightly coupled traces

?