LarryL’s blog - creating an ATX version of the Phoenix H5

[LarryL]

Hi,

First of all, I like to point out, that I have checked and discussed with @exxos upfront about my plans.
He set out some conditions:

1) the design is used for non-profit non-commercial aspects.
2) it resembles the H5 architecture as close as reasonably possible
3) it is documented in any text and on the PCB is based on the "exxos H5 architecture" or similar wording.
4) should be documented that I have given you permission under license to use the H5 design for you only.

I have - of course - fully agreed :dualthumbup:

Since I am not at all a professional PCB designer I like to share my ideas and plans with you here and seeking for feedback and possibly some advices.


So, how did it start and why the heck I am doing this?
…because I can (hopefully) and it’ll be fun :cheer:

Last year I have built an ATX ST
I was really pleased, having an ST in a large case to put extensions, drives, etc. inside
But the design has some drawbacks, which others tried to heal by various adapter PCBS, e.g. here at Chillichai.com

The ATX ST design files (Eagle) are free, so at some point I thought to set-up the design in KiCAD and change it to my needs.
I checked with the Designer (Daniel) and he confirmed that the design is free and I can do whatever I want with it.

But very soon I thought of adding some of the H5 elements into the design - simply because I liked them.
I also built an H5 last year, and this is a really excellent design.
Very quickly I realized, that I have somehow created a H5 in ATX format already :excited: with some additions from the ATX ST.
So, time to check with Exxos, if he would be OK with this approach.
Outcome: see above

So here we go - that’s where I am so far:

I transferred most of the H5 design elements into my KiCAD schematics, what I have left out from the H5 design is:

• 3V3 part and respective 68k DIP sockets

• only one 5V 68k DIP socket (space is tight on a micro ATX) and I have ISA slots…

• I do not plan for the MIDI S2 board (space constraints), so Exxos advised to go for the H4 audio

• no ROM port (space constraints) - see below

• I only use the PLCC versions of MMU/GLUE and I am using the DIP version of the MFC

• RAM is either SIMM or the original 4MB ATX RAM-PCB (http://ataripcb.pl/atari_st_atx_ram_board_1.html), so no Falcon RAM connectors

From the ATX specifics I re-used mainly:

• Eiffel for keyboard & Joysticks - but I've added the parts for the LCD and the temp.-sensor incl. fan again (missing on the ATX ST). Keyboard/Mouse ports use a stacked Mini-DIN6, Joystick ports are accessible via IDC10 ports

• Ports directly on the ATX board (in the respective ATX port area) are: Video-DIN13, MIDI-In/Out, Floppy-DIN14, Keyboard/Mouse-MiniDIN6, and a 5V barrel Jack (optional)

• STGA with its ISA-Slot for ET4000

• TOS2.06 decoder (TOS2.06 decoding in GAL as per ppera)

I added/changed a few smaller things:

• headers for some signals: ACSI10/ROM3/ROM4, and HSYNC/VSYNC/BLANK to easily add e.g. RGB2HDMI

• Soft power on for the ATX power supply, using a Attiny84

• I added a 2nd ISA slot - 1st one used for ET4000, 2nd can be used for a ROM-Port PCB (design is here https://chillichai.com/atari-st-micro-atx/ )

• I also changed the pinouts of the ports (COM/LPT/ACSI) to be "standard" (also described at the chillichai site) - for COM/LPT you can use standard IDC cables towards ISA brackets, and for ACSI it has two headers, one with standard pinout for Ultrasatan and another with the Mega ST internal pinout

• pretty much all 74 logic, as well as resistors, capacitors, diodes, transistors are now SMD - but all on the top layer (not on the bottom as in the original ATX ST design)

• I plan to let all the SMD parts be assembled by JLCPCB, but I tried to use „large enough“ footprints to allow hand-soldering

Right now I have completed the schematics and did a 1st component placing - seems to fit, but I have absolutely no idea if routing will succeed. :WTF:

ATX H5 draft.jpeg

I think I still need to optimize component placement to allow routing. And I also need to check if space and placement will allow extensions like ST536, or evtl. PiStorm, and if the headers for the ports, switches, LED, etc. are placed right.
And of course - the whole routing still needs to be done. But first I like to get the schematics stable!

Why do I share this here?
I am seeking your feedback on the design, of course. Especially:

• Shall I add some specific things (within the limits of available space on the ATX board)?

• Did I make some (stupid) mistakes in the design (I am not a professional on this)

• And I already have some questions :lol:

During next days I will go into some details on specific parts of the design, to ask my questions
So, looking forward to some feedback :shock:

Regards
Michael

[Steve]

Might be a silly question but is it possible to include NetUsbee hardware on the motherboard? It would be really nice to have a couple of USB ports and Ethernet direct. If there's no room for headers on the edge, then perhaps there could be some IDC headers instead.

[LarryL]

Might be a silly question but is it possible to include NetUsbee hardware on the motherboard? It would be really nice to have a couple of USB ports and Ethernet direct. If there's no room for headers on the edge, then perhaps there could be some IDC headers instead.

Ok, the feature creep is starting :lol:

I have not looked into NetUsbee so far (is the design free?)
But at least at the Chillichai.com site there is a solution described to connect a EtherNEC via the ROM-Port-ISA Card
That’s what I wanted to check next
My fear is, that the space on the ATX board is already pretty occupied - but the two ISA slots provide some flexibility…

[LarryL]

OK, lets start with a few general questions, which came up during implementing the design in KiCAD:

• all supporting caps are 1uF - usually I always see 100nF. Any specific reason to go for 1uF?

• The MMU bus isolators & buffers are specced as 74AC373 and 74ACT244 - in my H5 I see LS types, so I think both is OK, depending on availability

• the H5 design shows a separate 16MHz OSC for the HD GAL, but there is an option to use the existing 16MHz from the Shifter. Is the latter tested and proven, or shall I go for a separate OSC?

• for the FDD, the Drive1 signal only goes to the external DIN14, not to the internal IDC. Since an ATX housing has enough space, I would also wire the Drive 1 signal to the IDC. Any reason not to do this? Of course, then internal and external Floppy should not be used in parallel. I could add another jumper to select...

• in the H5 reset circuit, the reset signal is driven from 3V3. Do I need to change things, if I drive this from 5V?

• I have not seen any polarized caps (electrolytic, tantalum) in the H5 design (and also not on my H5 board) Is this observation correct, or did I miss something?

• the original H4 audio circuit is using a BC337, only available as THT. Is a BC817-40 (like in the video circuit) the right equivalent?

• the IDE circuit uses a 2N3906 to drive the reset line. I checked for a SMD equivalent and found BC857B. Good choice?

• for Keyboard&Mouse I use the Eiffel schematics. Do you see a need to add a RJ12 socket for e.g. a Mega ST keyboard?

• for all resistors and capacitors I will go for 0805 footprint (hand soldering possible). Only for the few 75R resistors, JLCPCB has only 0603 in their "basic parts list". Going for smaller footprints for all resistors and caps would save some space, but (at least for me) makes it quite impossible to hand solder. What do you think?

regards
Michael

[LarryL]

Might be a silly question but is it possible to include NetUsbee hardware on the motherboard? It would be really nice to have a couple of USB ports and Ethernet direct. If there's no room for headers on the edge, then perhaps there could be some IDC headers instead.

Ok, made a quick check - Design seems to be free
https://hardware.atari.org/netusbee/netus.htm

Would need some significant space on the PCB, not only for the ports.
Maybe this could be integrated on a new Cartridge-Port PCB (replacing the EtherNEC of the Chillichai.com design)

Need to check the design files in more detail at the weekend…

[atari030]

If I had the time that was close to top of the wish list. Brilliant.

RTC might be a pretty important feature too. I think Kodak80 did design a PCB for the ATX board that might work too.

[LarryL]

If I had the time that was close to top of the wish list. Brilliant.

RTC might be a pretty important feature too. I think Kodak80 did design a PCB for the ATX board that might work too.

RTC is part of the H5 design anyway, and of course part of this ATX version

And yes, AFAIK it is Kodak80 who designed the ISA adapter boards for the Cardridge Port
The later revisions include RTC but you can simply not solder the RTC components and only use the Cart Port

[atari030]

Cool. I will check that out. I'm part way through a ATX build atm and have been a bit sidetracked by a 2600jr build. Better get cracking before this comes to fruition.

[LarryL]

Cool. I will check that out. I'm part way through a ATX build atm and have been a bit sidetracked by a 2600jr build. Better get cracking before this comes to fruition.

This will take some time, until the design is ready and I can start routing the PCB
I am having a 24/7 job in parallel :mrgreen:

[atari030]

I know the feeling........ work is the curse of the serial hobbyist.