MiSTer FPGA Forum

Just for fun (Part 3)…

Inspired from the SNAC Accessory Converter and the IEC Support of the C64 Core I created together with dtimber this little Adapter PCB.
The Adapter converts the MiSTer FPGA User Port (Serial IO/SNAC) into a Commodore IEC/CBM (Serial) Bus Port.
Use the Adapter to connect a real Commodore Floppy 1541 or compatible devices (SD2IEC/PI1541) to your MiSTer.
Use it with compatible Cores like the C64 Core.

There is a PCB for Levelshifter & Voltage Regulator breakout boards and a tested Full-SMD PCB available.
Case by dtimber.

More Details here: https://github.com/venice1200/MiSTer_SNAC2IEC

Tested Hardware
Boards: Analog Board 6.1, Digital Board 1.2
IEC Devices: SD2IEC, PI1541, CBM 1541, CBM1541-II (Stock DOS & JiffyDOS), CBM 1571
Restrictions: Only one genuine Commodore device can be used at a time

User-Videos
https://youtu.be/zR52L662JqI
https://www.youtube.com/watch?v=zR52L662JqI
https://www.youtube.com/watch?v=jKdF6Q4ZU_g
https://www.youtube.com/watch?v=Q-g8Mt_xXnU

Retrobit's C64-Core Video about Kernal, SID, RS232, SNAC2IEC & more.
https://www.youtube.com/watch?v=LXGE7Ap88mE

Very cool Thanks to both of you

Thank you!! Very nice looking.

Awesome! I suppose this would work with the 1520 plotter as well, as it also uses the IEC connection.
I love how the housing looks similar to a tiny Commodore power brick.

EDIT: I've heard talk about one of the MiSTer hardware sellers planning to sell adapters like this, months ago, but didn't hear anything since.

LamerDeluxe wrote: ↑Thu Apr 07, 2022 7:35 am Awesome! I suppose this would work with the 1520 plotter as well, as it also uses the IEC connection.
I love how the housing looks similar to a tiny Commodore power brick.

EDIT: I've heard talk about one of the MiSTer hardware sellers planning to sell adapters like this, months ago, but didn't hear anything since.

Yes and its working, but just work with a single IEC device only. For multiple IEC device operation we would need to make changes in the core as we need 2 extra fpga lines. Anyway one single IEC device should be ok for most users.

I had two devices connected.
First the pi1541 and behind the sd2iec.

Good to hear, will test this design. Thx for your work.

The only Pin on the IEC Connector which is actualy not connected is Pin 1 (SERIAL SRQ) and is described as "not used" by the C64.
https://www.c64-wiki.com/wiki/Serial_Port

But the C128 use it with the 1571/1581, so the PCB needs a re-design for the C128 if needed.

Cool, so daisy-chaining works as well then, good to hear!

Have just ordered some boards and will test.

venice wrote: ↑Thu Apr 07, 2022 10:18 am I had two devices connected.
First the pi1541 and behind the sd2iec.

It would be interesting to see daisy chaining with real commodore devices. Pi1541 does include a buffer to the design in order to cope with real commodore devices, otherwise a level shifter alone can only drive one device.

raparici wrote: ↑Fri Apr 08, 2022 8:48 am

venice wrote: ↑Thu Apr 07, 2022 10:18 am I had two devices connected.
First the pi1541 and behind the sd2iec.

It would be interesting to see daisy chaining with real commodore devices. Pi1541 does include a buffer to the design in order to cope with real commodore devices, otherwise a level shifter alone can only drive one device.

Yes, I'm ordering the pcb to test and compare with our design, seems similar. I think one IEC (real) device would be enough for most users but would be interesting to daisy chain devices. Have several and can confirm it soon.

venice wrote: ↑Thu Apr 07, 2022 2:56 pm The only Pin on the IEC Connector which is actualy not connected is Pin 1 (SERIAL SRQ) and is described as "not used" by the C64.
https://www.c64-wiki.com/wiki/Serial_Port

But the C128 use it with the 1571/1581, so the PCB needs a re-design for the C128 if needed.

Would be possible to share the BOM file for the full SMD version? I dont seem to find it on the Github. Thanks!

Edit:
Nevermind. I got it! Thanks for sharing anyways!

Daniel8b wrote: ↑Fri Apr 08, 2022 9:15 am ..share the BOM file for the full SMD version? I dont seem to find it on the Github. Thanks!

Edit:
Nevermind. I got it! Thanks for sharing anyways!

Please post it and I will add it

venice wrote: ↑Fri Apr 08, 2022 1:39 pm Please post it and I will add it

Got it done in my head actually, but if Im not wrong should be something like this:

R1-R4: 0 ohm 0805 resistors (optional)
R5-R12: 10k 0805 resistors
C1-C3: 100nf 0805 capacitors
Q1-Q4: N-Channel SOT23 MOSFET transistors (BSS138 or similar)
U1: 3.3v LM1117 SOT223 regulator
J1: USB3 type A connector
J2: 6 pin DIN connector
J3: DC barrel connector (5.5/2.1 mm should be fine for most PSUs)

I dont have KiCAD installed so you might want to doublecheck my list

C1 - C3 shall be 22 uF. Please pay attention to buy a 1117 regulator which is stable with MLCCs caps (mentioned within datasheet).

Daniel8b wrote: ↑Fri Apr 08, 2022 2:48 pm …
I dont have KiCAD installed so you might want to doublecheck my list

Many Thx

Just as a note, the Full-SMD PCB is (currently) untested.

venice wrote: ↑Fri Apr 08, 2022 4:22 pm Many Thx

Just as a note, the Full-SMD PCB is (currently) untested.

I'll test it out and post my findings here. I have a couple of 1541s and some IEC2SD around...

Cheers!

Ok! I can confirm the SMD PBC is working fine. I will now test it with two devices to see how it goes.

Greets!

Please drop some pictures of your build!

Here is one:

@Daniel8b that looks very nice.
I'm looking forward to your test results daisy-chaining multiple iec devices.

NML32 wrote: ↑Fri Apr 22, 2022 4:04 pm @Daniel8b that looks very nice.
I'm looking forward to your test results daisy-chaining multiple iec devices.

I did a quick test with two 1541 (one 1541 and one 1541 II) and so far I was not able to get them running at the same time... Probably is too much for the level shifter to drive. But hey, one drive is already great to check out all those old disks!

Daniel8b wrote: ↑Fri Apr 22, 2022 4:42 pm

NML32 wrote: ↑Fri Apr 22, 2022 4:04 pm @Daniel8b that looks very nice.
I'm looking forward to your test results daisy-chaining multiple iec devices.

I did a quick test with two 1541 (one 1541 and one 1541 II) and so far I was not able to get them running at the same time... Probably is too much for the level shifter to drive. But hey, one drive is already great to check out all those old disks!

Agreed, one is better than none.

Daniel8b wrote: ↑Fri Apr 22, 2022 4:42 pm

NML32 wrote: ↑Fri Apr 22, 2022 4:04 pm @Daniel8b that looks very nice.
I'm looking forward to your test results daisy-chaining multiple iec devices.

I did a quick test with two 1541 (one 1541 and one 1541 II) and so far I was not able to get them running at the same time... Probably is too much for the level shifter to drive. But hey, one drive is already great to check out all those old disks!

Was one of the drives working?
Silly question, did you use different ID‘s for the drives?

Hey Venice! This is awesome, are you taking commissions to build these? Been thinking about trying to get things off my childhood disks + playing with print shop.

triangle wrote: ↑Mon May 02, 2022 4:04 am Hey Venice! This is awesome, are you taking commissions to build these?

No, but we got a request from two well known sellers we will see.

Depending on your location, it may be that someone has a board left for DIY. Ask around.

venice wrote: ↑Sun Apr 24, 2022 7:43 am Was one of the drives working?
Silly question, did you use different ID‘s for the drives?

Yes, I tried different IDs for each drive.

There was a combination (I belive having the older 1541 first on the daisy chain, but Im not sure now) that resulted in one drive working.

I received my SNAC2IEC built this week-end, this is really an amazing device. I've tested it with a real floppy and it works like a charm, next step will be to test with the SD2IEC device and also by using 2 devices to see if this works or not. But I'm already happy to see my real floppy drive connected to the Mister and got it working like on real hardware.