A8PicoCart - UnoCart on a Raspberry Pi Pico

[+mytek]

16 minutes ago, ivop said:

Series resistors don't help to protect the RP2040. It is voltage that overstress the internal transistors, not current. It might take days, weeks, months, but it will die.

On the contrary it is current that drives the break-down of the internal clamping diodes used as over voltage protection. Normally they are rated for 20 ma, but because of heat issues they really should be kept at 1 ma or below if sustained operation is key.

 

BITD, I built a power control system based upon a zero-crossing detector to minimize switching noise when the IGBT would get turned ON or OFF. This used nothing more than a high impedance resistor to look at the mains voltage which was several orders of magnitude above the input rating of the micro-controller I was using (6502). The idea was very similar to this article that MicroChip released: Atmel-2508-Zero-Cross-Detector_ApplicationNote_AVR182.pdf

 

That particular project where I incorporated the simple series resistor zero-crossing detector was used day in and day out for years without issue in a product controlling the rotation of X-Ray machine stators for medical usage. However we did have a 24 VAC transformer for line voltage isolation allowing us to reference ground on its output, and to serve as a power supply for several different analog and digital DC voltages needed through rectification and subsequent linear voltage regulators. Still the fact remained that we were feeding a much higher voltage into a low voltage processor input via a series resistor to limit the current to 1 ma.

 

33 minutes ago, ivop said:

It's not my intention to be a "party pooper", but I'm concerned that if I design something that sits on the bus 24/7 it's not solid enough for an XL machine.

I totally get it. And it's good that people point out such concerns

[ivop]

1 hour ago, mytek said:

On the contrary it is current that drives the break-down of the internal clamping diodes used as over voltage protection. Normally they are rated for 20 ma, but because of heat issues they really should be kept at 1 ma or below if sustained operation is key.

Sorry, I should have been clearer. The ARM ESD protection circuits are not traditional clamping diodes (except for the shared ADC pins), and are not meant for continuous overload, only short-lived ESD events.

 

Gate level oxide breakdown occurs at both over-voltage and over-current. When over-voltage goes over the oxide layers threshold it'll create a low-resistance path between gate and source/drain, which will result in a current spike, further damaging the transistor, unrelated to the initial current. The voltage threshold is generally measured with a very low current and slowly increasing the voltage until it breaks. The current threshold is measured by keeping the voltage constant within spec and upping the current until it breaks. That's how I understood it.

 

Edit: I only just now see you linked an Atmel document. AVRs (and PICs) have proper clamping diodes so your story is indeed prove that below 1mA it is safe to over-voltage

 

Edited December 22, 2023 by ivop

[+mytek]

1 hour ago, ivop said:

Sorry, I should have been clearer. The ARM ESD protection circuits are not traditional clamping diodes (except for the shared ADC pins), and are not meant for continuous overload, only short-lived ESD events.

 

Gate level oxide breakdown occurs at both over-voltage and over-current. When over-voltage goes over the oxide layers threshold it'll create a low-resistance path between gate and source/drain, which will result in a current spike, further damaging the transistor, unrelated to the initial current. The voltage threshold is generally measured with a very low current and slowly increasing the voltage until it breaks. The current threshold is measured by keeping the voltage constant within spec and upping the current until it breaks. That's how I understood it.

 

Edit: I only just now see you linked an Atmel document. AVRs (and PICs) have proper clamping diodes so your story is indeed prove that below 1mA it is safe to over-voltage

 

All good points, and it certainly appears that the manufacturer of the RP2040 wouldn't advise doing it. However it might just be one of those things that although not suggested, turns out to be OK.

 

The longer the present A8Pico Cart is out in the wild, the more we'll find out if it is a permissible application variance for our Atari 8-bit computers. Because I don't believe @electrotrains has any intention of changing the design at this point, and there will be plenty more made this way down the road.

 

If you scout around the internet you will find quite a few people pushing this same envelope with the RP2040.

 

 

[ivop]

4 minutes ago, mytek said:

All good points, and it certainly appears that the manufacturer of the RP2040 wouldn't advise doing it. However it might just be one of those things that although not suggested, turns out to be OK.

 

The longer the present A8Pico Cart is out in the wild, the more we'll find out if it is a permissible application variance for our Atari 8-bit computers. Because I don't believe @electrotrains has any intention of changing the design at this point, and there will be plenty more made this way down the road.

 

If you scout around the internet you will find quite a few people pushing this same envelope with the RP2040.

[YT Video]

Yes, we will see what happens in a year or so The video and all other projects without level shifters I have seen are without having the output pins pulled-high though. If I remember correctly @electrotrains developed it for an XE first? There it'll run fine according to Raspberry Pi's Eben Upton.

 

Here's another nice project (with level shifters though):

 

https://github.com/frntc/SIDKick-pico

 

It's a pity the RP2040 does not have enough GPIO pins to do one of our 40-pin VLSIs.

 

[+mytek]

59 minutes ago, ivop said:

Yes, we will see what happens in a year or so The video and all other projects without level shifters I have seen are without having the output pins pulled-high though. If I remember correctly @electrotrains developed it for an XE first? There it'll run fine according to Raspberry Pi's Eben Upton.

 

Here's another nice project (with level shifters though):

 

https://github.com/frntc/SIDKick-pico

Also my upcoming daughter board for the 576NUC+ uses the same A8Pico Cart aspect, with 4.7K pull-ups being the case for the data bus on the main computer board as well.

 

59 minutes ago, ivop said:

It's a pity the RP2040 does not have enough GPIO pins to do one of our 40-pin VLSIs.

Yeah there's certainly enough power to do it

[ndary]

On 5/24/2023 at 11:20 AM, electrotrains said:

Its the one described here - https://forums.raspberrypi.com/viewtopic.php?t=337976

I See its support ATR files, if you mount an ATR can you write to it?

[Beeblebrox]

2 hours ago, ndary said:

I See its support ATR files, if you mount an ATR can you write to it?

If you are taking about creating and mounting an ATR disk image then I don't think so.

 

Avg can do it because it can hook up to SIO using a special cable. And side3 can do it if you have u1mb installed. 

 

I could be wrong (correct me people if so), but I think you are only gonna get ATR read support. 

Edited December 23, 2023 by Beeblebrox

[electrotrains]

3 hours ago, ndary said:

I See its support ATR files, if you mount an ATR can you write to it?

Yes.

[Beeblebrox]

14 minutes ago, electrotrains said:

Yes.

Cool, I stand corrected.

[Mq.]

I know that atr files are used with restrictions, but actually the cartridge can already emulate a floppy drive and a mounted atr file. I wonder if it would be possible to add an external cable to the SIO socket and fully emulate the atr like the AVG cartridge does?

[Bee]

Anyone near Los Angeles have 2 extra purple picos?  I'd like to test 2 projects on them before ordering a batch.

 

If so PM me, plz.

 

Thank you 

[KRG-Rosa]

Can we run CAR files larger than 128kb, if so, can you tell me how and with what uf2 loader, because I suppose not the original one from Robin.Thank you.

 

Edited December 26, 2023 by KRG-Rosa

[Piotr D. Kaczorowski]

@electrotrains,

 

Is there an official PCBWAY or JLCPCB project share for ordering and purchasing? 

 

 

Edited December 26, 2023 by Piotr D. Kaczorowski

[Jfcatari]

On 12/23/2023 at 1:48 PM, Bee said:

Anyone near Los Angeles have 2 extra purple picos?  I'd like to test 2 projects on them before ordering a batch.

 

If so PM me, plz.

 

Thank you 

I bought 10 of these from Ali and they worked fine.  

 

https://www.aliexpress.us/item/3256804090698520.html?spm=a2g0o.order_list.order_list_main.5.4f321802HowIdo&gatewayAdapt=glo2usa

 

 

[+mytek]

32 minutes ago, Jfcatari said:

I bought 10 of these from Ali and they worked fine.  

 

https://www.aliexpress.us/item/3256804090698520.html?spm=a2g0o.order_list.order_list_main.5.4f321802HowIdo&gatewayAdapt=glo2usa

Me too

 

Shipping was cheaper than it would cost to ship within the same state, and the total cost all together for 10 pieces was $23 to my doorstep. Not bad for a lifetime supply 👍

[Piotr D. Kaczorowski]

Dear Friends,

 

A8PicoCart PCB should be 1.6mm or better 1.2mm ?  What is your recommendation about the thickness? 

 

Best,

Piotr

[Mq.]

Every cartridges are 1.6mm like a standard edge connectors. I can't believe you don't know it.

[Piotr D. Kaczorowski]

7 hours ago, Mq. said:

Every cartridges are 1.6mm like a standard edge connectors. I can't believe you don't know it.

To be honest, I haven't made cartridges myself yet. With a few original carts and the Ultimate Cart, SIDE3.1, and AVG, there hasn't been a need. However, the A8PicoCart project is particularly interesting to me due to the "software as hardware" approach and the use of MCU instead of FPGA. I've found some information online that in some cases, 1.2mm boards are used for Atari 2600 carts, hence the question about best practices.

[+mytek]

15 hours ago, Mq. said:

Every cartridges are 1.6mm like a standard edge connectors. I can't believe you don't know it.

There was a time that you didn't know this either

 

Sometimes we forget how much unique information there is to know about our A8 computers, with a lot of it being dependent upon an individual's personal involvement in a given area of interest.

[Fred_M]

For me, the best way is to upload the gerber files first to PCBWay. That way all data is filled out correctly. The only change I make is to bevel the fingers 20%.

 

Hope this helps 🙂

[Piotr D. Kaczorowski]

I usually carry out my projects with JLCPCB. They offer great prices, and currently, there's even a $5 promotion until the end of the year. You need to grab a coupon for that. Despite the popularity of PCBWAY, I think JLCPCB has significantly better prices. There are, of course, some differences, and here I wanted to ask people who can correct 3D STL projects. It works in PCBWAY, but maybe it could work in JLCPCB as well. I'm having trouble with the acceptance of the A8PicoCart logo specifically.

 

Could someone take a look at this and help?

 

The dimensions seem to be okay, but they are in reverse order.

Edited December 27, 2023 by Piotr D. Kaczorowski

[Piotr D. Kaczorowski]

36 minutes ago, Fred_M said:

For me, the best way is to upload the gerber files first to PCBWay. That way all data is filled out correctly. The only change I make is to bevel the fingers 20%.

 

Hope this helps 🙂

 

"30°finger chamfered" - in JLCPCB..  Would be ok?

[Mq.]

1 hour ago, mytek said:

16 hours ago, Mq. said:

Every cartridges are 1.6mm like a standard edge connectors. I can't believe you don't know it.

There was a time that you didn't know this either

 

Sometimes we forget how much unique information there is to know about our A8 computers, with a lot of it being dependent upon an individual's personal involvement in a given area of interest.

@mytek yes, I know it, but in this particular case I know Piotr from Polish forums. I know he is electronic engineer which is fixing Atari, and he designs electronic devices for Atari, extensions, etc. That's why I wrote what I wrote

[Fred_M]

8 hours ago, Piotr D. Kaczorowski said:

 

"30°finger chamfered" - in JLCPCB..  Would be ok?

No, 30% is too much. I started my PCBWay with 30% and was warned by the staff that the edge of the PCB would become too thin. I ordered mine with 20% bevel and they are great 🙂

Edited December 28, 2023 by Fred_M

[Bee]

Is there a way to get a.ATR to run on power up?  Its in basic and has an autorun.sys that works from the menu.  

 

Thank you