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View topic - Minimal slot 2 cartridge design

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  • Joined: 06 Mar 2022
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Post Posted: Wed Apr 05, 2023 11:04 am
thatawesomeguy wrote
I was looking at getting some of these made today, seems the SST39SF040A is in short supply, is there an alternate flash that could be used?

Haven't checked the pinout is exactly the same, but this might be an option?

https://octopart.com/search?q=MX29F400CBTI-70G&currency=USD&specs=0

EDIT: here's a line on the SST that might work for you if it ships okay?
https://www.mouser.co.uk/ProductDetail/Microchip-Technology/SST39SF040-55-4C-WHE-T?qs=uHi2%2FQoPa5BOvOWz7HmMdQ%3D%3D
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  • Joined: 03 Mar 2022
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Post Posted: Wed Apr 05, 2023 12:24 pm
thatawesomeguy wrote
I was looking at getting some of these made today, seems the SST39SF040A is in short supply, is there an alternate flash that could be used?


There are plenty of them in Mouser:
* https://www.mouser.es/ProductDetail/Microchip-Technology/SST39SF040-55-4C-WHE-T?...
* https://www.mouser.es/ProductDetail/Microchip-Technology/SST39SF040-55-4C-WHE?qs...

Also stock is expected to enter on Digikey 24th April, so I hope there is no problem with this chip.

Also I do not know why I put the final 'A' in the value, maybe a typo on my side, the part is SST39SF040 (any speed variant in TSOP format should be OK).
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  • Joined: 24 Mar 2021
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Post Posted: Wed Apr 05, 2023 5:43 pm
Microchip's supply of 5V parallel NOR flash had some fairly significant supply chain problems over the past three years due to no longer having their own fab.

If you go to their own storefront (microchipdirect) they have hardly any stock on hand, so it's almost entirely luck as to which distributor you can buy from.

You could look at octopart
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Post Posted: Sun Apr 09, 2023 4:02 pm
Ordered 5 Rev.B PCBs on JLCPCB. Will take some time to arrive since I payed the cheap shipping. Most of the cost is just fees. The component cost per board is about $5, being most of it the flash memory chip.
20230409_175845.png (86.15 KB)
20230409_175845.png

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Post Posted: Thu Apr 20, 2023 9:21 am
I've also got some boards on order.

Obviously, I need to build your programmer as well, do you have the BOM or component list for it?
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Post Posted: Fri Apr 21, 2023 7:42 am
Here is the repository: https://gitlab.com/doragasu/mw-prog/

You can download the artifact package including gerbers, BoM, CPL files, etc. in the package repository: https://gitlab.com/doragasu/mw-prog/-/packages
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Post Posted: Fri Apr 21, 2023 8:51 am
I managed to extract the BOM out of Kicad, C5 C9 C10 C11
don't have any value, just "NP" which I'm assuming just means non-polarised, what value should these caps be?
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Post Posted: Fri Apr 21, 2023 9:04 am
I also received today the partially populated cart PCB (just need to wait for the flash chip), and unpopulated programmer PCB which I'll create the order for components once I know all the values.

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Post Posted: Fri Apr 21, 2023 1:02 pm
thatawesomeguy wrote
I managed to extract the BOM out of Kicad, C5 C9 C10 C11
don't have any value, just "NP" which I'm assuming just means non-polarised, what value should these caps be?

Could mean Not Placed as in DNP = Do Not Place maybe?
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Post Posted: Fri Apr 21, 2023 2:15 pm
Exactly, I usually say Not Populated.
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Post Posted: Fri Apr 21, 2023 2:21 pm
BTW, did you order the boards at JLCPCB? Just in case you don't know (I didn't until recently) you can order through their parts library the components they do not have stocked, and have them also assembled (I ordered boards with all components assembled, including the flash chip). They only charge $1 (or $1.50, I cannot remember) for management of the entire parts order.
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Post Posted: Fri Apr 21, 2023 11:19 pm
I didn't want to wait for the backorder, it was quicker to order direct and just solder myself.
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Post Posted: Tue May 02, 2023 9:05 am
Revision C released. It removes D1 by changing the default drive in RA14 to the A14 signal through a resistor. I have not sent this board for fabrication, but I have done the changes on a Revision B board and it works perfect.

As usual, you can grab the design files on the package registry of the repository.

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Post Posted: Tue May 02, 2023 9:47 am
out of curiosity, making it both slot-1 and slot-2 SEGA mapper compatible would it be possible without major updates or it pretty much means doubling all the parts?
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Post Posted: Tue May 02, 2023 10:41 am
I have not put too much thought into it, but it would require adding at least two more chips: another register, and some more decoding logic.
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Post Posted: Tue May 02, 2023 1:15 pm
yeah, as I supposed, apart from the Flash chip pretty much everything else needs to be present twice :|
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Post Posted: Tue May 02, 2023 1:55 pm
Maybe we could achieve it just doubling the chips, but in the worst case we could have to add more than double, because I took some shortcuts that are only valid if only slot 2 is used. E.g., my cart maps the slot 2 register in the full $E000 to $FFFF range to save decoding logic. If we want to support also slot 1, we need to at least add the least significant bit into the decoding equation (so writes to even addresses in the $E000 to $FFFF range reach slot 1 register while writes to odd addresses in the same range reach the slot 2 register).
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Post Posted: Tue May 02, 2023 2:28 pm
Yeah, I thought so too. Fortunately this is just one bit, maybe it could be used to enable either one or the other chip which holds the registers
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Post Posted: Tue Jun 13, 2023 8:37 am
Interested in testing this board out but got a couple questions:

- What angle should the bevelling be done at? (couldn't find any info on that in the repo files)

- What's the optional component for? (C1)
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Post Posted: Wed Jun 14, 2023 4:28 am
- 30°
- C1 is not an "optional part", it's a global decoupling cap.
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Post Posted: Wed Jun 14, 2023 10:13 am
Thanks ichigobankai :)

The BoM list that part as an "optional part" and "do not fit" :-/

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Post Posted: Wed Jun 14, 2023 10:31 am
Yes, doragasu got the board to work without it, however personally I would always advise to fit a bulk capacitor because why not really - they cost basically nothing at all and it can only help.

I'd go for between 1uF and 10uF.
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Post Posted: Wed Jun 14, 2023 10:39 am
Ok, thanks for the info :)
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Post Posted: Wed Jun 14, 2023 1:45 pm
Yes, boards will work without but thats electronically incorrect. They are needed for noises/current spikes/stability.
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Post Posted: Fri Jun 30, 2023 2:19 pm
Decoupling (and in general terms PDN, Power Delivery Network design) is a very complex topic and broad assumptions are generally wrong. That said, these 5V logic boards using modern chips running at low frequencies are very robust and for this specific board, I would be surprised if it is really needed. The MLCC capacitors for the individual chips should be more than enough.

To back this up, I have to say that I have tested several boards for quite a few hours without a single issue, including erasing and programming the chip from the console itself (that should be the most stressful task since it is when the flash chip draws the most power).

Anyway, if you want to be on the safe side, you can always assemble the capacitor, and it will cost just a few cents, so ¯\_(ツ)_/¯
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